Heterodimeric neurotoxic phospholipases A2—The first proteins from venom of recently established species Vipera nikolskii: Implication of venom composition in viper systematics

Analysis of intra-specific variations in the venom of individual snakes based on Raman spectroscopy

The knowledge of variations in the composition of venoms from different snakes is important from both theoretical and practical points of view, in particular, at developing and selecting an antivenom. Many studies on this topic are conducted with pooled venoms, while the existence and significance of variations in the composition of venoms between individual snakes of the same species are emphasized by many authors. It is important to study both inter- and intra-specific, including intra-population, venom variations, because intra-specific variations in the venom composition may affect the effectiveness of antivenoms as strongly as inter-specific. In this work, based on venom Raman spectroscopy with principal component analysis, we assessed the variations in venoms of individual snakes of the Vipera nikolskii species from two populations and compared these intra-specific variations with inter-specific variations (with regard to the other related species). We demonstrated intra-specific (inter- and intra-population) differences in venom compositions which are smaller than inter-specific variations. We also assessed the compositions of V. nikolskii venoms from two populations to explain inter-population differences. The method used is rapid and requires virtually no preparation of samples, used in extremely small quantities, allowing the venoms of individual snakes to be analyzed. In addition, the method is informative and capable of detecting fairly subtle differences in the composition of venoms.

Effects of the Heterodimeric Neurotoxic Phospholipase A2 from the Venom of Vipera nikolskii on the Contractility of Rat Papillary Muscles and Thoracic Aortas

Phospholipases A2 (PLA2s) are a large family of snake toxins manifesting diverse biological effects, which are not always related to phospholipolytic activity. Snake venom PLA2s (svPLA2s) are extracellular proteins with a molecular mass of 13-14 kDa. They are present in venoms in the form of monomers, dimers, and larger oligomers. The cardiovascular system is one of the multiple svPLA2 targets in prey organisms. The results obtained previously on the cardiovascular effects of monomeric svPLA2s were inconsistent, while the data on the dimeric svPLA2 crotoxin from the rattlesnake Crotalus durissus terrificus showed that it significantly reduced the contractile force of guinea pig hearts. Here, we studied the effects of the heterodimeric svPLA2 HDP-1 from the viper Vipera nikolskii on papillary muscle (PM) contractility and the tension of the aortic rings (ARs). HDP-1 is structurally different from crotoxin, and over a wide range of concentrations, it produced a long-term, stable, positive inotropic effect in PMs, which did not turn into contractures at the concentrations studied. This also distinguishes HDP-1 from the monomeric svPLA2s, which at high concentrations inhibited cardiac function. HDP-1, when acting on ARs preconstricted with 10 μM phenylephrine, induced a vasorelaxant effect, similar to some other svPLA2s. These are the first indications of the cardiac and vascular effects of true vipers' heterodimeric svPLA2s.

Fifty Years of Animal Toxin Research at the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry RAS

This review covers briefly the work carried out at our institute (IBCh), in many cases in collaboration with other Russian and foreign laboratories, for the last 50 years. It discusses the discoveries and studies of various animal toxins, including protein and peptide neurotoxins acting on the nicotinic acetylcholine receptors (nAChRs) and on other ion channels. Among the achievements are the determination of the primary structures of the α-bungarotoxin-like three-finger toxins (TFTs), covalently bound dimeric TFTs, glycosylated cytotoxin, inhibitory cystine knot toxins (ICK), modular ICKs, and such giant molecules as latrotoxins and peptide neurotoxins from the snake, as well as from other animal venoms. For a number of toxins, spatial structures were determined, mostly by 1H-NMR spectroscopy. Using this method in combination with molecular modeling, the molecular mechanisms of the interactions of several toxins with lipid membranes were established. In more detail are presented the results of recent years, among which are the discovery of α-bungarotoxin analogs distinguishing the two binding sites in the muscle-type nAChR, long-chain α-neurotoxins interacting with α9α10 nAChRs and with GABA-A receptors, and the strong antiviral effects of dimeric phospholipases A2. A summary of the toxins obtained from arthropod venoms includes only highly cited works describing the molecules' success story, which is associated with IBCh. In marine animals, versatile toxins in terms of structure and molecular targets were discovered, and careful work on α-conotoxins differing in specificity for individual nAChR subtypes gave information about their binding sites.

Cytogenetic Analysis of the Bimodal Karyotype of the Common European Adder, Vipera berus (Viperidae)

Vipera berus is the species with the largest range of snakes on Earth and one of the largest among reptiles in general. It is also the only snake species found in the Arctic Circle. Vipera berus is the most involved species of the genus Vipera in the process of interspecific hybridization in nature. The taxonomy of the genus Vipera is based on molecular markers and morphology and requires clarification using SC-karyotyping. This work is a detailed comparative study of the somatic and meiotic karyotypes of V. berus, with special attention to DNA and protein markers associated with synaptonemal complexes. The karyotype of V. berus is a remarkable example of a bimodal karyotype containing both 16 large macrochromosomes and 20 microchromosomes. We traced the stages of the asynchronous assembly of both types of bivalents. The number of crossing-over sites per pachytene nucleus, the localization of the nucleolar organizer, and the unique heterochromatin block on the autosomal bivalent 6-an important marker-were determined. Our results show that the average number of crossing-over sites per pachytene nucleus is 49.5, and the number of MLH1 sites per bivalent 1 reached 11, which is comparable to several species of agamas.

Biochemistry and toxicology of proteins and peptides purified from the venom of Vipera berus berus

The isolation and characterization of individual snake venom components is important for a deeper understanding of the pathophysiology of envenomation and for improving the therapeutic procedures of patients. It also opens possibilities for the discovery of novel toxins that might be useful as tools for understanding cellular and molecular processes. The variable venom composition, toxicological and immunological properties of the common vipers (Vipera berus berus) have been reviewed. The combination of venom gland transcriptomics, bottom-up and top-down proteomics enabled comparison of common viper venom proteomes from multiple individuals. V. b. berus venom contains proteins and peptides belonging to 10–15 toxin families: snake venom metalloproteinase, phospholipases A₂ (PLA₂), snake venom serine proteinase, aspartic protease, L-amino acid oxidase (LAAO), hyaluronidase, 5′-nucleotidase, glutaminyl-peptide cyclotransferase, disintegrin, C-type lectin (snaclec), nerve growth factor, Kunitz type serine protease inhibitor, snake venom vascular endothelial growth factor, cysteine-rich secretory protein, bradykinin potentiating peptide, natriuretic peptides. PLA₂ and LAAO from V. b. berus venom produce more pronounced cytotoxic effects in cancer cells than normal cells, via induction of apoptosis, cell cycle arrest and suppression of proliferation. Proteomic data of V. b. berus venoms from different parts of Russia and Slovakian Republic have been compared with analogous data for Vipera nikolskii venom. Proteomic studies demonstrated quantitative differences in the composition of V. b. berus venom from different geographical regions. Differences in the venom composition of V. berus were mainly driven by the age, sex, habitat and diet of the snakes. The venom variability of V. berus results in a loss of antivenom efficacy against snakebites. The effectiveness of antibodies is discussed. This review presents an overview with a special focus on different toxins that have been isolated and characterized from the venoms of V. b. berus. Their main biochemical properties and toxic actions are described.

•

Vipera berus berus venom composition is variable among different populations.

•

Venom contains about 15 protein/peptide families.

•

It disturbs blood coagulation inducing pro- or anticoagulant effects.

•

Venom contains different types of blood factor X activators.

•

PLA₂ and L-amino acid oxidase produce cytotoxic effects in cancer cells.

Anti-HIV Activity of Snake Venom Phospholipase A2s: Updates for New Enzymes and Different Virus Strains

Since the beginning of the HIV epidemic, lasting more than 30 years, the main goal of scientists was to develop effective methods for the prevention and treatment of HIV infection. Modern medicines have reduced the death rate from AIDS by 80%. However, they still have side effects and are very expensive, dictating the need to search for new drugs. Earlier, it was shown that phospholipases A2 (PLA2s) from bee and snake venoms block HIV replication, the effect being independent on catalytic PLA2 activity. However, the antiviral activity of human PLA2s against Lentiviruses depended on catalytic function and was mediated through the destruction of the viral membrane. To clarify the role of phospholipolytic activity in antiviral effects, we analyzed the anti-HIV activity of several snake PLA2s and found that the mechanisms of their antiviral activity were similar to that of mammalian PLA2. Our results indicate that snake PLA2s are capable of inhibiting syncytium formation between chronically HIV-infected cells and healthy CD4-positive cells and block HIV binding to cells. However, only dimeric PLA2s had pronounced virucidal and anti-HIV activity, which depended on their catalytic activity. The ability of snake PLA2s to inactivate the virus may provide an additional barrier to HIV infection. Thus, snake PLA2s might be considered as candidates for lead molecules in anti-HIV drug development.

Snake venom phospholipase A2s exhibit strong virucidal activity against SARS-CoV-2 and inhibit the viral spike glycoprotein interaction with ACE2

The COVID-19 pandemic caused by SARS-CoV-2 requires new treatments both to alleviate the symptoms and to prevent the spread of this disease. Previous studies demonstrated good antiviral and virucidal activity of phospholipase A₂s (PLA₂s) from snake venoms against viruses from different families but there was no data for coronaviruses. Here we show that PLA₂s from snake venoms protect Vero E6 cells against SARS-CoV-2 cytopathic effects. PLA₂s showed low cytotoxicity to Vero E6 cells with some activity at micromolar concentrations, but strong antiviral activity at nanomolar concentrations. Dimeric PLA₂ from the viper Vipera nikolskii and its subunits manifested especially potent virucidal effects, which were related to their phospholipolytic activity, and inhibited cell-cell fusion mediated by the SARS-CoV-2 spike glycoprotein. Moreover, PLA₂s interfered with binding both of an antibody against ACE2 and of the receptor-binding domain of the glycoprotein S to 293T/ACE2 cells. This is the first demonstration of a detrimental effect of PLA₂s on β-coronaviruses. Thus, snake PLA₂s are promising for the development of antiviral drugs that target the viral envelope, and could also prove to be useful tools to study the interaction of viruses with host cells.

PLA2 Inhibitor Varespladib as an Alternative to the Antivenom Treatment for Bites from Nikolsky's Viper Vipera berus nikolskii

Although envenoming by a small East European species of viper is rarely severe, and only exceptionally fatal, lack of specific antivenom stocks in a few areas within this region and possible severe side effects of antivenom application leave most bites to be treated only with antihistamines and supportive therapy. Varespladib is an effective inhibitor of snake phospholipase, and, as such, it could be considered as first-line therapy. The Nikolsky’s viper venom contains an extremely high concentration of phospholipase A2 (PLA₂), responsible for the toxic effects of the venom, as well as minor amounts of other toxins. If Varespladib can successfully inhibit PLA₂ activity, the Nikolsky’s viper could be one of the first venomous snakes having an antitoxin-specific treatment regimen. To assess that, Varespladib was administered alone subcutaneously to adult male CD-1 mice (8 mg/kg) and compared to mice exposed to Vipera berus nikolskii crude venom (8 mg/kg = 10 LD₅₀) or a combination of Varespladib and the same amount of the venom. Experimental animals were monitored for the presence of envenoming symptoms and mortality for 48 h after injection. Eighty percent of mice receiving both Varespladib and venom survived, while 100% of the control group receiving venom alone died within 4 h. Experimental results are consistent with Varespladib acting as an effective antitoxin in the mouse model against Nikolsky’s viper venom. Further studies are needed under experimental conditions that more closely resemble natural envenoming (i.e., delayed administration).

Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins

Snake venoms possess lethal activities against different organisms, ranging from bacteria to higher vertebrates. Several venoms were shown to be active against protozoa, however, data about the anti-protozoan activity of cobra and viper venoms are very scarce. We tested the effects of venoms from several snake species on the ciliate Tetrahymena pyriformis. The venoms tested induced T. pyriformis immobilization, followed by death, the most pronounced effect being observed for cobra Naja sumatrana venom. The active polypeptides were isolated from this venom by a combination of gel-filtration, ion exchange and reversed-phase HPLC and analyzed by mass spectrometry. It was found that these were cytotoxins of the three-finger toxin family. The cytotoxins from several cobra species were tested and manifested toxicity for infusorians. Light microscopy revealed that, because of the cytotoxin action, the infusorians’ morphology was changed greatly, from teardrop-like to an almost spherical shape, this alteration being accompanied by a leakage of cell contents. Fluorescence microscopy showed that the fluorescently labelled cytotoxin 2 from cobra N. oxiana was localized mainly at the membrane of killed infusorians, indicating that cytotoxins may kill T. pyriformis by causing membrane rupture. This work is the first evidence of the antiprotozoal activity of cobra venom cytotoxins, as demonstrated by the example of the ciliate T. pyriformis.

Scorpion toxins interact with nicotinic acetylcholine receptors

Neurotoxins are among the main components of scorpion and snake venoms. Scorpion neurotoxins affect voltage-gated ion channels, while most snake neurotoxins target ligand-gated ion channels, mainly nicotinic acetylcholine receptors (nAChRs). We report that scorpion venoms inhibit α-bungarotoxin binding to both muscle-type nAChR from Torpedo californica and neuronal human α7 nAChR. Toxins inhibiting nAChRs were identified as OSK-1 (α-KTx family) from Orthochirus scrobiculosus and HelaTx1 (κ-KTx family) from Heterometrus laoticus, both being blockers of voltage-gated potassium channels. With an IC₅₀ of 1.6 μm, OSK1 inhibits acetylcholine-induced current through mouse muscle-type nAChR heterologously expressed in Xenopus oocytes. Other well-characterized scorpion toxins from these families also bind to Torpedo nAChR with micromolar affinities. Our results indicate that scorpion neurotoxins present target promiscuity.

Individual variability of venom from the European adder (Vipera berus berus) from one locality in Eastern Hungary

We have revealed intra-population variability among venom samples from several individual European adders (Vipera berus berus) within a defined population in Eastern Hungary. Individual differences in venom pattern were noticed, both gender-specific and age-related, by one-dimensional electrophoresis. Gelatin zymography demonstrated that these individual venoms have different degradation profiles indicating varying protease activity in the specimens from adders of different ages and genders. Some specimens shared a conserved region of substrate degradation, while others had lower or extremely low protease activity. Phospholipase A₂ activity of venoms was similar but not identical. Interspecimen diversity of the venom phospholipase A₂-spectra (based on the components' molecular masses) was detected by MALDI-TOF MS. The lethal toxicity of venoms (LD₅₀) also showed differences among individual snakes. Extracted venom samples had varying neuromuscular paralysing effect on chick biventer cervicis nerve-muscle preparations. The paralysing effect of venom was lost when calcium in the physiological salt solution was replaced by strontium; indicating that the block of twitch responses to nerve stimulation is associated with the activity of a phospholipase-dependent neurotoxin. In contrast to the studied V. b. berus venoms from different geographical regions so far, this is the first V. b. berus population discovered to have predominantly neurotoxic neuromuscular activity. The relevance of varying venom yields is also discussed. This study demonstrates that individual venom variation among V. b. berus living in particular area of Eastern Hungary might contribute to a wider range of clinical manifestations of V. b. berus envenoming than elsewhere in Europe.

Quantitative Proteomic Analysis of Venoms from Russian Vipers of Pelias Group: Phospholipases A₂ are the Main Venom Components

Venoms of most Russian viper species are poorly characterized. Here, by quantitative chromato-mass-spectrometry, we analyzed protein and peptide compositions of venoms from four Vipera species (V. kaznakovi, V. renardi, V. orlovi and V. nikolskii) inhabiting different regions of Russia. In all these species, the main components were phospholipases A₂, their content ranging from 24% in V. orlovi to 65% in V. nikolskii. Altogether, enzyme content in venom of V. nikolskii reached ~85%. Among the non-enzymatic proteins, the most abundant were disintegrins (14%) in the V. renardi venom, C-type lectin like (12.5%) in V. kaznakovi, cysteine-rich venom proteins (12%) in V. orlovi and venom endothelial growth factors (8%) in V. nikolskii. In total, 210 proteins and 512 endogenous peptides were identified in the four viper venoms. They represented 14 snake venom protein families, most of which were found in the venoms of Vipera snakes previously. However, phospholipase B and nucleotide degrading enzymes were reported here for the first time. Compositions of V. kaznakovi and V. orlovi venoms were described for the first time and showed the greatest similarity among the four venoms studied, which probably reflected close relationship between these species within the “kaznakovi” complex.

Inhibition of nicotinic acetylcholine receptors, a novel facet in the pleiotropic activities of snake venom phospholipases A2

Phospholipases A2 represent the most abundant family of snake venom proteins. They manifest an array of biological activities, which is constantly expanding. We have recently shown that a protein bitanarin, isolated from the venom of the puff adder Bitis arietans and possessing high phospholipolytic activity, interacts with different types of nicotinic acetylcholine receptors and with the acetylcholine-binding protein. To check if this property is characteristic to all venom phospholipases A2, we have studied the capability of these enzymes from other snakes to block the responses of Lymnaea stagnalis neurons to acetylcholine or cytisine and to inhibit α-bungarotoxin binding to nicotinic acetylcholine receptors and acetylcholine-binding proteins. Here we present the evidence that phospholipases A2 from venoms of vipers Vipera ursinii and V. nikolskii, cobra Naja kaouthia, and krait Bungarus fasciatus from different snake families suppress the acetylcholine- or cytisine-elicited currents in L. stagnalis neurons and compete with α-bungarotoxin for binding to muscle- and neuronal α7-types of nicotinic acetylcholine receptor, as well as to acetylcholine-binding proteins. As the phospholipase A2 content in venoms is quite high, under some conditions the activity found may contribute to the deleterious venom effects. The results obtained suggest that the ability to interact with nicotinic acetylcholine receptors may be a general property of snake venom phospholipases A2, which add a new target to the numerous activities of these enzymes.

Azemiopsin from Azemiops feae viper venom, a novel polypeptide ligand of nicotinic acetylcholine receptor

Azemiopsin, a novel polypeptide, was isolated from the Azemiops feae viper venom by combination of gel filtration and reverse-phase HPLC. Its amino acid sequence (DNWWPKPPHQGPRPPRPRPKP) was determined by means of Edman degradation and mass spectrometry. It consists of 21 residues and, unlike similar venom isolates, does not contain cysteine residues. According to circular dichroism measurements, this peptide adopts a β-structure. Peptide synthesis was used to verify the determined sequence and to prepare peptide in sufficient amounts to study its biological activity. Azemiopsin efficiently competed with α-bungarotoxin for binding to Torpedo nicotinic acetylcholine receptor (nAChR) (IC₅₀ 0.18 ± 0.03 μm) and with lower efficiency to human α7 nAChR (IC₅₀ 22 ± 2 μm). It dose-dependently blocked acetylcholine-induced currents in Xenopus oocytes heterologously expressing human muscle-type nAChR and was more potent against the adult form (α1β1ϵδ) than the fetal form (α1β1γδ), EC₅₀ being 0.44 ± 0.1 μm and 1.56 ± 0.37 μm, respectively. The peptide had no effect on GABA_A (α1β3γ2 or α2β3γ2) receptors at a concentration up to 100 μm or on 5-HT₃ receptors at a concentration up to 10 μm. Ala scanning showed that amino acid residues at positions 3–6, 8–11, and 13–14 are essential for binding to Torpedo nAChR. In biological activity azemiopsin resembles waglerin, a disulfide-containing peptide from the Tropidechis wagleri venom, shares with it a homologous C-terminal hexapeptide, but is the first natural toxin that blocks nAChRs and does not possess disulfide bridges.

Epidemiology of snakebites in Europe: a systematic review of the literature

Snakebites are rare medical emergency cases in Europe but may sometimes be severe and lead to complications. A better knowledge of snakebite epidemiology may help health authorities to better understand therapeutic requirements, especially concerning antivenoms, and thus improve treatment of snakebite. An extensive literature search for studies and articles published between 1970 and 2010 was performed. Both indexed and non-indexed articles were examined, the analysis of which took into account the heterogeneity between the studies and weighted the studies according to size of the study population covered. Most of the articles involved hospitalized patients who represented more than 90% of snakebites. Incidence, mortality and population at risk were estimated after stratification into three regions (northern, central and southern Europe) based both on viper species distribution and climatic characteristics. There was no significant variation in incidence from the north to the south of Europe. In the whole of Europe, including European Russia and Turkey, the annual number of snakebite cases was estimated at 7992 [CI 95% = 6860-9178] bites, out of which approximately 15% were considered severe (grade 3). These bites usually occurred between May and September, with a more dispersed distribution in southern Europe. The average number of deaths per annum was 4 [0.7-7.7]. Children and male victims are more affected, contrary to what one would expect given their respective proportion in the entire population. Both upper and lower limb bites were recorded at an equal frequency while the bites in other parts of the body were very rare. Immunotherapy was prescribed in one out of three snakebites in Europe, with a very high geographical variability, in spite of excellent tolerance, at least considering highly-purified immunoglobulin fragments. Snakebites are uncommon in Europe but can cause life-threatening envenomation. Fragments of highly-purified immunoglobulins are now very well tolerated and dramatically reduce both severity and mortality of snakebites when used in treatment.

[Molecular cloning and analysis of cDNA sequences encoding serine proteinase and Kunitz type inhibitor in venom gland of Vipera nikolskii viper]

Serine proteinases and Kunitz type inhibitors are widely represented in venoms of snakes from different genera. During the study of the venoms from snakes inhabiting Russia we have cloned cDNAs encoding new proteins belonging to these protein families. Thus, a new serine proteinase called nikobin was identified in the venom gland of Vipera nikolskii viper. By amino acid sequence deduced from the cDNA sequence, nikobin differs from serine proteinases identified in other snake species. Nikobin amino acid sequence contains 15 unique substitutions. This is the first serine proteinase of viper from Vipera genus for which a complete amino acid sequence established. The cDNA encoding Kunitz type inhibitor was also cloned. The deduced amino acid sequence of inhibitor is homologous to those of other proteins from that snakes of Vipera genus. However there are several unusual amino acid substitutions that might result in the change of biological activity of inhibitor.

cDNA cloning, structural, and functional analyses of venom phospholipases A₂ and a Kunitz-type protease inhibitor from steppe viper Vipera ursinii renardi

Snake venom phospholipases A₂ (PLA₂s) display a wide array of biological activities and are each characteristic to the venom. Here, we report on the cDNA cloning and characterization of PLA₂s from the steppe viper Vipera ursinii renardi venom glands. Among the five distinct PLA₂ cDNAs cloned and sequenced, the most common were the clones encoding a basic Ser-49 containing PLA₂ (Vur-S49). Other clones encoded either ammodytin analogs I1, I2d and I2a (designated as Vur-PL1, Vur-PL2 and Vur-PL3, respectively) or an ammodytoxin-like PLA₂ (Vurtoxin). Additionally, a novel Kunitz-type trypsin inhibitor for this venom species was cloned and sequenced. Comparison of these PLA₂ and Kunitz inhibitor sequences with those in the sequence data banks suggests that the viper V. u. renardi is closely related to Vipera ammodytes and Vipera aspis. Separation of V. u. renardi venom components by gel-filtration and ion-exchange chromatography showed the presence of many PLA₂ isoforms. Remarkably, the most abundant PLA₂ isolated was Vur-PL2 while Vur-S49 analog was in very low yield. There are great differences between the proportion of cDNA clones and that of the proteins isolated. Two Vur-PL2 isoforms (designated as Vur-PL2A and Vur-PL2B) indistinguishable by masses, peptide mass fingerprinting, N-terminal sequences and CD spectroscopy were purified from the pooled venom. However, when rechromatographed on cation-exchanger, Vur-PL2A showed only one peak corresponding to Vur-PL2B, suggesting the existence of conformers for Vur-PL2. Vur-PL2B was weakly cytotoxic to rat pheochromocytoma PC12 cells and showed both strong anticoagulant and anti-platelet activities. This is the first case of a strong anticoagulating ammodytin I analog in Vipera venom.