Biological activities ofSynanceja horrida (stonefish) venom

Expression of Recombinant Stonustoxin Alpha Subunit and Preparation of polyclonal antiserum for Stonustoxin Neutralization Studies

Stonustoxin (SNTX) is a lethal protein found in stonefish venom, responsible for many of the symptoms associated with stonefish envenomation. To counter stonefish venom challenges, antivenom is a well-established and effective solution. In this study, we aimed to produce the recombinant alpha subunit protein of Stonustoxin from Synanceia horrida and prepare antibodies against it The SNTXα gene sequence was optimized for E. coli BL21 (DE3) expression and cloned into the pET17b vector. Following purification, the recombinant protein was subcutaneously injected into rabbits, and antibodies were extracted from rabbit´s serum using a G protein column As a result of codon optimization, the codon adaptation index for the SNTXα cassette increased to 0.94. SDS-PAGE analysis validated the expression of SNTXα, with a band observed at 73.5 kDa with a yield of 60 mg/l. ELISA results demonstrated rabbits antibody titers were detectable up to a 1:256,000 dilution. The isolated antibody from rabbit´s serum exhibited a concentration of 1.5 mg/ml, and its sensitivity allowed the detection of a minimum protein concentration of 9.7 ng. In the neutralization assay the purified antibody against SNTXα protected mice challenged with 2 LD50. In conclusion, our study successfully expressed the alpha subunit of Stonustoxin in a prokaryotic host, enabling the production of antibodies for potential use in developing stonefish antivenom.

Fish Cytolysins in All Their Complexity

The majority of the effects observed upon envenomation by scorpaenoid fish species can be reproduced by the cytolysins present in their venoms. Fish cytolysins are multifunctional proteins that elicit lethal, cytolytic, cardiovascular, inflammatory, nociceptive, and neuromuscular activities, representing a novel class of protein toxins. These large proteins (MW 150–320 kDa) are composed by two different subunits, termed α and β, with about 700 amino acid residues each, being usually active in oligomeric form. There is a high degree of similarity between the primary sequences of cytolysins from different fish species. This suggests these molecules share similar mechanisms of action, which, at least regarding the cytolytic activity, has been proved to involve pore formation. Although the remaining components of fish venoms have interesting biological activities, fish cytolysins stand out because of their multifunctional nature and their ability to reproduce the main events of envenomation on their own. Considerable knowledge about fish cytolysins has been accumulated over the years, although there remains much to be unveiled. In this review, we compiled and compared the current information on the biochemical aspects and pharmacological activities of fish cytolysins, going over their structures, activities, mechanisms of action, and perspectives for the future.

A Chromosome-Level Genome Assembly of the Mandarin Fish (Siniperca chuatsi)

The mandarin fish, Siniperca chuatsi, is an economically important perciform species with widespread aquaculture practices in China. Its special feeding habit, acceptance of only live prey fishes, contributes to its delicious meat. However, little is currently known about related genetic mechanisms. Here, we performed whole-genome sequencing and assembled a 758.78 Mb genome assembly of the mandarin fish, with the scaffold and contig N50 values reaching 2.64 Mb and 46.11 Kb, respectively. Approximately 92.8% of the scaffolds were ordered onto 24 chromosomes (Chrs) with the assistance of a previously established genetic linkage map. The chromosome-level genome contained 19,904 protein-coding genes, of which 19,059 (95.75%) genes were functionally annotated. The special feeding behavior of mandarin fish could be attributable to the interaction of a variety of sense organs (such as vision, smell, and endocrine organs). Through comparative genomics analysis, some interesting results were found. For example, olfactory receptor (OR) genes (especially the beta and delta types) underwent a significant expansion, and endocrinology/vision related npy, spexin, and opsin genes presented various functional mutations. These may contribute to the special feeding habit of the mandarin fish by strengthening the olfactory and visual systems. Meanwhile, previously identified sex-related genes and quantitative trait locis (QTLs) were localized on the Chr14 and Chr17, respectively. 155 toxin proteins were predicted from mandarin fish genome. In summary, the high-quality genome assembly of the mandarin fish provides novel insights into the feeding habit of live prey and offers a valuable genetic resource for the quality improvement of this freshwater fish.

Utilisation of compounds from venoms in drug discovery

Difficult drug targets are becoming the normal course of business in drug discovery, sometimes due to large interacting surfaces or only small differences in selectivity regions. For these, a different approach is merited: compounds lying somewhere between the small molecule and the large antibody in terms of many properties including stability, biodistribution and pharmacokinetics. Venoms have evolved over millions of years to be complex mixtures of stable molecules derived from other somatic molecules, the stability comes from the pressure to be ready for delivery at a moment's notice. Snakes, spiders, scorpions, jellyfish, wasps, fish and even mammals have evolved independent venom systems with complex mixtures in their chemical arsenal. These venom-derived molecules have been proven to be useful tools, such as for the development of antihypotensive angiotensin converting enzyme (ACE) inhibitors and have also made successful drugs such as Byetta® (Exenatide), Integrilin® (Eptifibatide) and Echistatin. Only a small percentage of the available chemical space from venoms has been investigated so far and this is growing. In a new era of biological therapeutics, venom peptides present opportunities for larger target engagement surface with greater stability than antibodies or human peptides. There are challenges for oral absorption and target engagement, but there are venom structures that overcome these and thus provide substrate for engineering novel molecules that combine all desired properties. Venom researchers are characterising new venoms, species, and functions all the time, these provide great substrate for solving the challenges presented by today's difficult targets.

The Geographic Distribution, Venom Components, Pathology and Treatments of Stonefish (Synanceia spp.) Venom

Stonefish are regarded as one of the most venomous fish in the world. Research on stonefish venom has chiefly focused on the in vitro and in vivo neurological, cardiovascular, cytotoxic and nociceptive effects of the venom. The last literature review on stonefish venom was published over a decade ago, and much has changed in the field since. In this review, we have generated a global map of the current distribution of all stonefish (Synanceia) species, presented a table of clinical case reports and provided up-to-date information about the development of polyspecific stonefish antivenom. We have also presented an overview of recent advancements in the biomolecular composition of stonefish venom, including the analysis of transcriptomic and proteomic data from Synanceia horrida venom gland. Moreover, this review highlights the need for further research on the composition and properties of stonefish venom, which may reveal novel molecules for drug discovery, development or other novel physiological uses.

Getting stoned: Characterisation of the coagulotoxic and neurotoxic effects of reef stonefish (Synanceia verrucosa) venom

The reef stonefish (Synanceia verrucosa) is a venomous fish which causes excruciatingly painful envenomations. While some research on the pathophysiology and functions of the venom have been conducted, there are still some gaps in the understanding of the venom effects due to the extreme lability of fish venom toxins and the lack of available testing platforms. Here we set out to assess new functions of the venom whilst also attempting to address some unclear pathophysiological effects from previous literature. Utilising a biolayer interferometry assay, our results highlight that the venom binds to the orthosteric site of the α-1 nicotinic acetylcholine receptor as well as the domain IV of voltage-gated Ca²⁺ (Ca_V1.2) channel mimotopes. Both these results add some clarity to the previously ambiguous literature. We further assessed the coagulotoxic effects of the venom using thromboelastography and Stago STA-R Max coagulation analyser assays. We reveal that the venom produced anticoagulant activity and significantly delayed time until clot formation of recalcified human plasma which is likely through the degradation of phospholipids. There was a difference between fresh and lyophilised venom activity toward the nicotinic acetylcholine receptor mimotopes and coagulation assays, whilst no difference was observed in the activity toward the domain IV of Ca_V1.2 mimotopes. This research adds further insights into the neglected area of fish venom whilst also highlighting the extreme labile nature of fish venom toxins.

Is stonefish Synanceia verrucosa envenomation potentially lethal?

Stonefish sting lethality in man has been scarcely documented since the middle of the 20th century. We report three clinical cases, including one fatality, emphasizing the cardiovascular toxicity of the Synanceia verrucosa venom, and its potentially lethal effects. All clinical data have been recently collected in New Caledonia and French Polynesia.

Biochemical, Hematological Effects and Complications of Pseudosynanceia Melanostigma Envenoming

Objectives

Venomous fishes have different pharmacological effects and are useful. Among the venomous fish, stonefishes; especially Pseudosynanceia melanostigma has various pharmacological effects on the nervous, muscular and cardiovascular system of humans. In this study, toxicological characteristics, some blood effects, pharmacological and enzymatic properties of Pseudosynanceia melanostigma venom was investigated.

Methods

Crude venom purified by using gel filtration chromatography and the molecular weights of the venom and its fractions were estimated. The approximate LD values of this venom were determinedand the effects of LD50 dose on the blood of rabbits were studied. Hemolytic and Hemorrhagic activity of the venom sample was determined. In this case coagulation tests were performed.

Results

The LD50 of the Pseudosynanceia melanostigma crude venom was also determined to be 194.54 μg/mouse. The effect of two doses of LD50 showed a non-significant differences decrease in RBCs and MCV. In other cases, the results showed significant differences in WBC, Plt, Hb, MCH, MCHC and HCT; also it’s showed a significant decrease. WBC count showed a significant increase with two doses of LD50 groups. The prothrombin time and partial prothrombin time were increased after venom treatment. As well as bleeding and clotting time were increased. According to the results, a minimum dose for Haemorrhagic effect 40 μg was obtained.

Conclusion

Venom of Pseudosynanceia melanostigma has inhibitory effect on platelet aggregation that can be used to design and develop of anticoagulant drugs.

Combined proteomic and functional analysis reveals rich sources of protein diversity in skin mucus and venom from the Scorpaena plumieri fish

The biological activities observed upon envenomation by Scorpaena plumieri could be linked to both the venom and the skin mucus. Through a proteomic/functional approach we analyzed protein composition and biological activities of the venom and skin mucus. We identified 885 proteins: 722 in the Venomous Apparatus extracts (Sp-VAe) and 391 in the Skin Mucus extract (Sp-SMe), with 494 found exclusively in Sp-VAe, being named S. plumieri Venom Proteins (Sp-VP), while 228 were found in both extracts. The majority of the many proteins identified were not directly related to the biological activities reported here. Nevertheless, some were classified as toxins/potentially interesting molecules: lectins, proteases and protease inhibitors were detected in both extracts, while the pore-forming toxin and hyaluronidase were associated with Sp-VP. Proteolytic and anti-microbial activities were linked to both extracts, while the main toxic activities - cardiovascular, inflammatory, hemolytic and nociceptive - were elicited only by Sp-VAe. Our study provided a clear picture on the composition of the skin mucus and the venom. We also show that the classic effects observed upon envenomation are produced by molecules from the venomous gland. Our results add to the growing catalogue of scorpaeniform fish venoms and their skin mucus proteins.

SIGNIFICANCE

In this study a large number of proteins - including classical and non-classical toxins - were identified in the venomous apparatus and the skin mucus extracts of the Scorpaena plumieri fish through shotgun proteomic approach. It was shown that the toxic effects observed upon envenomation are elicited by molecules originated from the venomous gland. These results add to the growing catalogue of scorpaeniform fish venoms and their skin mucus proteins - so scarcely explored when compared to the venoms and bioactive components of terrestrial animals. Data are available via ProteomeXchange with identifier PXD009983.

Biochemical and histopathological effects of the stonefish (Synanceia verrucosa) venom in rats

The Reef Stonefish (Synanceia verrucosa) is one of the most dangerous venomous fish known, and has caused occasional human fatalities. The present study was designed to examine some of the pathological effects of the venom from this fish in Sprague Dawley rats. Crude venom was extracted from venom glands of the dorsal spines of stonefish specimens collected from coral reefs in the Gulf of Aqaba (in the northeastern branch of the Red Sea). The rats were given intramuscular injections of the venom and acute toxicity and effect on selected serum marker enzymes as well as normal architecture of vital organs were evaluated. The rat 24 h LD50 was 38 μg/kg body weight. The serum biochemical markers; alanine transaminase (ALT), lactate dehydrogenase (LDH) and creatine kinase (CK) increased after 6 h of administration of a sub lethal dose of the venom and remained significantly raised at 24 h. Amylase levels also significantly increased after venom injection. The venom caused histological damage manifested as an interstitial hemorrhage, inflammatory cell infiltration, and necrosis. The demonstrated rises in the levels of different critical biochemical parameters in the serum may have led to the observed abnormal morphological changes in these organs. These results may account for some of the clinical manifestations observed in victims of stonefish envenomation. Thus, the presented data provide further in vivo evidence of the stonefish toxic effects that may threaten human life and call for the need for special measures to be considered.

The Cardiovascular and Neurotoxic Effects of the Venoms of Six Bony and Cartilaginous Fish Species

Fish venoms are often poorly studied, in part due to the difficulty in obtaining, extracting, and storing them. In this study, we characterize the cardiovascular and neurotoxic effects of the venoms from the following six species of fish: the cartilaginous stingrays Neotrygon kuhlii and Himantura toshi, and the bony fish Platycephalus fucus, Girella tricuspidata, Mugil cephalus, and Dentex tumifrons. All venoms (10–100 µg/kg, i.v.), except G. tricuspidata and P. fuscus, induced a biphasic response on mean arterial pressure (MAP) in the anesthetised rat. P. fucus venom exhibited a hypotensive response, while venom from G. tricuspidata displayed a single depressor response. All venoms induced cardiovascular collapse at 200 µg/kg, i.v. The in vitro neurotoxic effects of venom were examined using the chick biventer cervicis nerve-muscle (CBCNM) preparation. N. kuhlii, H. toshi, and P. fucus venoms caused concentration-dependent inhibition of indirect twitches in the CBCNM preparation. These three venoms also inhibited responses to exogenous acetylcholine (ACh) and carbachol (CCh), but not potassium chloride (KCl), indicating a post-synaptic mode of action. Venom from G. tricuspidata, M. cephalus, and D. tumifrons had no significant effect on indirect twitches or agonist responses in the CBCNM. Our results demonstrate that envenoming by these species of fish may result in moderate cardiovascular and/or neurotoxic effects. Future studies aimed at identifying the molecules responsible for these effects could uncover potentially novel lead compounds for future pharmaceuticals, in addition to generating new knowledge about the evolutionary relationships between venomous animals.

A review on the Scorpaena plumieri fish venom and its bioactive compounds

The most poisonous fish species found along the Brazilian coast is the spotted scorpionfish Scorpaena plumieri. Though hardly ever life-threatening to humans, envenomation by S. plumieri can be quite hazardous, provoking extreme pain and imposing significant socioeconomic costs, as the victims may require days to weeks to recover from their injuries. In this review we will walk the reader through the biological features that distinguish this species as well as the current epidemiological knowledge related to the envenomation and its consequences. But above all, we will discuss the challenges involved in the biochemical characterization of the S. plumieri venom and its compounds, focusing then on the successful isolation and pharmacological analysis of some of the bioactive molecules responsible for the effects observed upon envenomation as well as on experimental models. Despite the achievement of considerable progress, much remains to be done, particularly in relation to the non-proteinaceous components of the venom. Therefore, further studies are necessary in order to provide a more complete picture of the venom’s chemical composition and physiological effects. Given that fish venoms remain considerably less studied when compared to terrestrial venoms, the exploration of their full potential opens a myriad of possibilities for the development of new drug leads and tools for elucidating the complex physiological processes.

Stonefish toxin defines an ancient branch of the perforin-like superfamily

The lethal factor in stonefish venom is stonustoxin (SNTX), a heterodimeric cytolytic protein that induces cardiovascular collapse in humans and native predators. Here, using X-ray crystallography, we make the unexpected finding that SNTX is a pore-forming member of an ancient branch of the Membrane Attack Complex-Perforin/Cholesterol-Dependent Cytolysin (MACPF/CDC) superfamily. SNTX comprises two homologous subunits (α and β), each of which comprises an N-terminal pore-forming MACPF/CDC domain, a central focal adhesion-targeting domain, a thioredoxin domain, and a C-terminal tripartite motif family-like PRY SPla and the RYanodine Receptor immune recognition domain. Crucially, the structure reveals that the two MACPF domains are in complex with one another and arranged into a stable early prepore-like assembly. These data provide long sought after near-atomic resolution insights into how MACPF/CDC proteins assemble into prepores on the surface of membranes. Furthermore, our analyses reveal that SNTX-like MACPF/CDCs are distributed throughout eukaryotic life and play a broader, possibly immune-related function outside venom.

Bioactive components in fish venoms

Animal venoms are widely recognized excellent resources for the discovery of novel drug leads and physiological tools. Most are comprised of a large number of components, of which the enzymes, small peptides, and proteins are studied for their important bioactivities. However, in spite of there being over 2000 venomous fish species, piscine venoms have been relatively underrepresented in the literature thus far. Most studies have explored whole or partially fractioned venom, revealing broad pharmacology, which includes cardiovascular, neuromuscular, cytotoxic, inflammatory, and nociceptive activities. Several large proteinaceous toxins, such as stonustoxin, verrucotoxin, and Sp-CTx, have been isolated from scorpaenoid fish. These form pores in cell membranes, resulting in cell death and creating a cascade of reactions that result in many, but not all, of the physiological symptoms observed from envenomation. Additionally, Natterins, a novel family of toxins possessing kininogenase activity have been found in toadfish venom. A variety of smaller protein toxins, as well as a small number of peptides, enzymes, and non-proteinaceous molecules have also been isolated from a range of fish venoms, but most remain poorly characterized. Many other bioactive fish venom components remain to be discovered and investigated. These represent an untapped treasure of potentially useful molecules.

Proteinaceous toxins from three species of scorpaeniform fish (lionfish Pterois lunulata, devil stinger Inimicus japonicus and waspfish Hypodytes rubripinnis): close similarity in properties and primary structures to stonefish toxins

The crude toxins from three species of venomous fish (lionfish Pterois lunulata, devil stinger Inimicus japonicus and waspfish Hypodytes rubripinnis) belonging to the order Scorpaeniformes exhibited mouse-lethal, hemolytic, edema-forming and nociceptive activities. In view of the antigenic cross-reactivity with the stonefish toxins, the primary structures of the stonefish toxin-like toxins from the three scorpaeniform fish were determined by cDNA cloning using primers designed from the highly conserved sequences of the stonefish toxins. Based on the data obtained in gel filtration, immunoblotting and cDNA cloning, each toxin was judged to be a 160 kDa heterodimer composed of 80 kDa α- and β-subunits. The three scorpaeniform fish toxins contain a B30.2/SPRY domain (∼200 amino acid residues) in the C-terminal region of each subunit, as reported for the toxins from two species of lionfish and two species of stonefish. With respect to the amino acid sequence similarity, the scorpaeniform fish toxins are divided into the following two groups: toxins from three species of lionfish and those from devil stinger, two species of stonefish and waspfish. The phylogenetic tree generated also clearly supports the classification of the toxins.

Renal Lysosomal Functions on Exposure to Scatophagus argus Venom in Experimental Mice

ABSTRACT Scatophagus argus venom was extracted by homogenization and centrifugation. The lysosome-enriched fraction of mice kidney was isolated by differential centrifugation. To study the effect of S. argus venom on lysosomal membrane stability, acid phosphatase and cathepsin D, the two marker enzymes for lysosome, were assayed. In the renal lysosomal enriched fraction incubated with different concentrations of venom and at various time intervals, in vivo and in vitro studies were done. Studies reveal that with increasing concentration of venom and time, the activity of the enzymes increased, which showed that the membrane integrities decreased for both in vitro and in vivo studies. The activity of the enzymes acid phosphatase and cathepsin D showed a dose-dependent relationship with S. argus venom.

A potent vasoactive cytolysin isolated from Scorpaena plumieri scorpionfish venom

A new vasoactive cytolytic toxin, referred to as Sp-CTx, has been purified from the venom of the scorpionfish Scorpaena plumieri by a combination of gel filtration and anion exchange chromatographies. An estimation of Sp-CTx native molecular mass, performed by size exclusion chromatography, demonstrated that it is a 121 kDa protein. Further physicochemical studies revealed its glycoproteic nature and dimeric constitution, comprising subunits of approximately 65 kDa (MALDI-TOF-MS). Such protein has proved to possess a potent hemolytic activity on washed rabbit erythrocytes (EC(50) 0.46 nM), whose effect was strongly reduced after treatment with antivenom raised against stonefish venom -Synanceja trachynis (SFAV). This cross-reactivity has been confirmed by western blotting. Like S. plumieri whole venom (100 microg/mL), Sp-CTx (1-50 nM) caused a biphasic response on phenylephrine pre-contracted rat aortic rings, characterized by an endothelium- and dose-dependent relaxation phase followed by a contractile phase. The vasorelaxant activity has been abolished by l-NAME, demonstrating the involvement of nitric oxide on the response. We report here the first isolation of a cytolytic/vasoactive protein from scorpionfish venom and the data provided suggest structural and functional similarities between Sp-CTx and previously published stonefish hemolytic toxins.

Biological and biochemical properties of Scatophagus argus venom

Scatophagus argus of the family Scatophagidae inflicts painful wounds in fishermen during handling. The clinical picture is characterized by excruciating and persistent local pain disproportionate to the size of injury, redness, swelling and a throbbing sensation that extends to the limbs, followed by dizziness. The biological properties of the S. argus venom were studied to assess its risk and lethal factors with regard to human welfare. In contrast to other fish venoms, S. argus showed relatively low LD50 (9.8 mg/kg via i.p.). Haemolytic activity in human erythrocytes was recorded. Platelet lysis expressed as LDH activity of lysed cells was dose dependent. S. argus venom failed to induce any clot in human plasma. No PLA(2) activity was found in S. argus venom. Mild proteolytic activity was observed. The injection of venom in mice produced lesions and nociception, which were not inhibited by antihistamine pheniramine maleate, suggesting that histamine was not involved in the inflammatory process. The increase in serum creatine kinase activity indicated myotoxicity. Cytotoxicity on HeLa cells was observed. The spectrum of activity in experimental animals of S. argus crude venom resembles those of other fish venoms previously studied and well correlated to the systemic manifestations that are described for S. argus envenomation.

Biological properties of the venom from the scorpionfish (Scorpaena plumieri) and purification of a gelatinolytic protease

In this work we describe some biological properties and a partial biochemical characterization of the Scorpanea plumieri crude venom. The fresh venom induced a decrease in blood pressure, cardiac and respiratory frequency, and exhibited hemorrhagic, hemolytic and proteolytic activities. The LD(50) (i.v. mouse) was 0.28 mg/kg. The pharmacological activities were found to be very unstable and this fact could be associated with proteolytic activity. Enzymes which hydrolyze casein and gelatin were found in this venom. A gelatinolytic protease (Sp-GP) was purified to homogeneity from S. plumieri venom through a combination of three chromatographic steps: gel filtration on Sephacryl S-200; ion exchange on DEAE-cellulose and reverse-phase/HPLC on a Vydac C4 column. The purified protease was approximately 2% of the whole protein in the soluble crude venom. The molecular mass of the Sp-GP scorpionfish gelatinase estimated by SDS-PAGE was around 80,000 Da under reducing conditions and 72,000 Da under non-reducing conditions. Attempts to determine the N-terminal sequence by automatic Edman degradation were unsuccessful, probably due to blockage of the N-terminal group. Gelatinolytic activity was optimal at pH 7-8. This is the first report of the isolation and characterization of a scorpionfish venom protease.

Marine antivenoms

There is an enormous diversity and complexity of venoms and poisons in marine animals. Fatalities have occurred from envenoming by sea snakes, jellyfish, venomous fish such as stonefish, cone snails, and blue-ringed octopus. Deaths have also followed ingestion of toxins in shellfish, puffer fish (Fugu), and ciguatoxin-containing fish. However antivenoms are generally only available for envenoming by certain sea snakes, the major Australian box jellyfish (Chironex fleckeri) and stonefish. There have been difficulties in characterizing the toxins of C. fleckeri venom, and there are conflicting animals studies on the efficacy of C. fleckeri antivenom. The vast majority of C. fleckeri stings are not life-threatening, with painful skin welts the major finding. However fatalities that do occur usually do so within 5 to 20 minutes of the sting. This unprecedented rapid onset of cardiotoxicity in clinical envenoming suggests that antivenom may need to be given very early (within minutes) and possibly in large doses if a life is to be saved. Forty years of anecdotal experience supports the beneficial effect of stonefish antivenom in relieving the excruciating pain after stonefish spine penetration. It remains uncertain whether stonefish antivenom is efficacious in stings from spines of other venomous fish, and the recommendation of giving the antivenom intramuscularly needs reassessment.

Bioactive proteins from stonefish venom

1. Of all the venomous fish known, the stonefish is one of the most commonly encountered by man. Studies on its venom started in the 1950s, but little work was performed after that until several groups revived interest in the venom in the 1980s after easier accessibility to the fish. 2. Stonefish venom is a mixture of proteins, containing several enzymes, including hyaluronidase of high specific activity. A purified stonefish hyaluronidase has been characterized. 3. Several of the effects of the crude venom have been isolated to a protein lethal factor that has cytolytic, neurotoxic and hypotensive activity. This protein is stonustoxin from Synanceja horrida, trachynilysin from Synanceja trachynis and verrucotoxin from Synanceja verrucosa. 4. The biochemical properties and activities of these protein lethal factors are reviewed.

The pharmacological activity of fish venoms

Venomous creatures have been the source of much recent research in the effort to find novel physiological tools and pharmaceuticals. However, due to the technical difficulties with obtaining and storing venom extracts, the venoms of marine animals, particularly fish, remain a largely untapped source of novel compounds. The most potent effects of piscine venoms are on the cardiovascular system. All piscine venoms produce profound cardiovascular changes, both in vitro and in vivo, including the release of nitric oxide from endothelial cells, smooth muscle contraction, and differing effects on atria. Although there is a complex balance between different components of the venom response, similarities exist between the responses to the venoms of all species of fish. In addition to their cardiovascular effects, piscine venoms possess neuromuscular activity. Once again, the activities of most piscine venoms are very similar, usually consisting of a depolarising action on both nerve and muscle cells. Most piscine venoms have potent cytolytic activity, and it seems likely that this activity is the mechanism behind many of their cardiovascular and neuromuscular effects. Piscine venoms all seem to share similar activity, probably as a result of evolving for a common purpose, and cross-reactivity with stonefish antivenom, both functionally in experimental models and in Western immunoblotting analysis, suggesting that piscine venoms may also possess structural similarities in addition to their functional similarities.

Effects of trachynilysin, a protein isolated from stonefish (Synanceia trachynis) venom, on frog atrial heart muscle

The effects of trachynilysin (TLY), a protein toxin isolated from stonefish (Synanceia trachynis) venom, were studied on the electrical and mechanical activities of frog atrial fibres. TLY (1 microg/ml) hyperpolarized the membrane, shortened the action potential (AP) duration (APD), exerted a negative inotropic effect and elicited contracture. These effects did not develop in the presence of atropine. TLY shortened the APD of fibres isolated from a frog completely paralyzed with botulinum type A toxin, in the presence of Ca2+ but not when Ca2+ was replaced by Sr2+. TLY increased the basal and the peak of the fluorescence ratio of stimulated fibres loaded with fura-2. Confocal laser scanning microscopy revealed the existence of a diffuse innervation in atrial tissue. Our results suggest that TLY enhances the release of acetylcholine from atrial cholinergic nerve terminals and activates indirectly muscarinic receptors leading to a shortening of APD. They also show that the mechanical effects induced by TLY are due to an increase of the Ca2+ influx and to a rise in intracellular Ca2+ levels which leads to (i) a slowing of the Na+/Ca2+ exchange activity, which accounts for the contracture and (ii) the activation of a Ca2+-dependent K+ current involved in the APD shortening.

Dose-dependent cardiovascular and neuromuscular effects of stonefish (Synanceja trachynis) venom

There has been recent debate regarding the labile nature of stonefish venoms and the pharmacology of their breakdown products. The present study examined the cardiovascular and neuromuscular effects of lyophilised venom, and conducted a preliminary investigation of freshly milked venom. Lyophilised venom (20 microg/ml) caused endothelium-dependent relaxation in rat aortae that was abolished by atropine (0.1 microM). In contrast, an endothelium-independent contractile response occurred in porcine coronary arteries. However, in the presence of atropine (10 nM), this became a relaxation response which was attenuated by the B2 antagonist FR-173657 (0.1 microM) or by a combination of idazoxan (1 microM) and propranolol (1 microM). In rat isolated atria, lyophilised venom (4 microg/ml) caused a biphasic inotropic response consisting of an initial decrease, and then increase, in force which were attenuated by atropine (0.5 microM) and propranolol (5 microM), respectively. The increase in force produced by venom was unaffected by reserpine pre-treatment suggesting a direct action at adrenoceptors. In the anaesthetised rat, lyophilised venom (1-300 microg/kg, i.v.), caused a dose-dependent depressor response, with a subsequent pressor response at higher concentrations (30-300 microg/kg, i.v.). In the presence of atropine (1 mg/kg, i.v.), the depressor response to venom was abolished, a transient pressor response unmasked and the secondary pressor response augmented. In the additional presence of prazosin (50 microg/kg, i.v.), the transient pressor response was abolished and the secondary pressor response attenuated. Lyophilised venom had no significant effect on nerve-evoked (10 microg/ml) or directly-evoked (100 microg/ml) twitches of the chick biventer cervicis muscle preparation. Milked venom (1 microl/ml) caused a biphasic response (i.e., an initial relaxation followed by contraction) in rat aortae, a contraction in porcine coronary arteries, complete cessation of rat isolated atrial activity and markedly inhibited both nerve-evoked and directly-evoked twitches of the chick biventer cervicis muscle preparation. In the anaesthetised rat, milked venom (15 microl/kg, i.v.) caused immediate cardiovascular collapse. It appears that the cardiovascular effects of stonefish venom are mediated by a dose-dependent action at muscarinic receptors and adrenoceptors.

The role of tryptophan residues in the hemolytic activity of stonustoxin,a lethal factor from stonefish (Synanceja horrida) venom

Stonustoxin (SNTX) is a pore-forming cytolytic lethal factor, isolated from the venom of the stonefish Synanceja horrida, that has potent hemolytic activity. The role of tryptophan residues in the hemolytic activity of SNTX was investigated. Oxidation of tryptophan residues of SNTX with N-bromosuccinimide (NBS) resulted in loss of hemolytic activity. Binding of 8-anilino-1-naphthalenesulphonate (ANS) to SNTX resulted in occlusion of tryptophan residues that resulted in loss of hemolytic activity. Circular dichroism and fluorescence studies indicated that ANS binding resulted in a conformational change of SNTX, in particular, a relocation of surface tryptophan residues to the hydrophobic interior. NBS-modification resulted in oxidised surface tryptophan residues that did not relocate to the hydrophobic interior. These results suggest that native surface tryptophan residues play a pivotal role in the hemolytic activity of STNX, possibly by being an essential component of a hydrophobic surface necessary for pore-formation. This study is the first report on the essentiality of tryptophan residues in the activity of a lytic and lethal factor from a fish venom.

Enzyme and biochemical studies of stonefish (Synanceja trachynis) and soldierfish (Gymnapistes marmoratus) venoms

Venoms from the scorpaeniformes Synanceja trachynis and Gymnapistes marmoratus were quantitatively analyzed for enzymic activity. S. trachynis venom displayed significantly higher hyaluronidase activity than G. marmoratus venom, and G. marmoratus venom displayed significantly higher levels of esterase, acid phosphatase, alkaline phosphatase and phosphodiesterase activity. No detectable quantities of phospholipase A2 activity were found in G. marmoratus venom. SDS-polyacrylamide gel electrophoresis of S. trachynis venom indicated the presence of 6 protein bands (20 kDa-295 kDa). G. marmoratus venom displayed 8 protein bands (11 kDa-109 kDa).

Role of free thiol groups in the biological activities of stonustoxin, a lethal factor from stonefish (Synanceja horrida) venom

Stonustoxin (SNTX) is a two-subunit protein purified from the venom of a stonefish, Synanceia horrida. It has potent lethal activity and is also a membrane pore-forming cytolysin. The role of thiol groups in the biological activities of SNTX was investigated. Both the hemolytic and lethal activities of SNTX were potentiated by the reducing agent, dithiothreitol (DTT). The hemolytic activity of SNTX was sensitive to the modification of thiol groups by 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). The loss of haemolytic activity correlated with the number of thiol groups that were titrated with DTNB. Thiol modification of SNTX with DTNB also inhibited its lethality. These inhibitory effects of thiol modification could be reversed by reduction with DTT. It was also found that the haemolytic activity of SNTX could not be inhibited by cholesterol. These observations indicate that free thiol groups play an important role in the haemolytic activity and lethality of SNTX but unlike other thiol-activated cytolysins, SNTX was not inhibited by cholesterol. Thus, SNTX may represent a new class of cytolytic toxin.

Haemolytic activity of stonustoxin from stonefish (Synanceja horrida) venom: pore formation and the role of cationic amino acid residues

Stonustoxin (SNTX) is a two-subunit protein toxin purified from the venom of the stonefish (Synanceja horrida), which induces potent haemolytic activity. We examined the pore-forming property of this non-enzymic protein by an osmotic protection assay. SNTX-induced haemolysis was completely prevented by osmotic protectants of adequate size [poly(ethylene) glycol 3000; molecular diameter approx. 3.2 nm]. Uncharged molecules of smaller size, such as raffinose and poly(ethylene) glycol 1000-2000, failed to protect against cell lysis. These findings indicate that SNTX induces the formation of hydrophilic pores in the cell membrane, which results in the lysis of erythrocytes. Since cationic residues contribute significantly to the cytolytic activity of several other pore-forming toxins, we examined the role of positively charged lysine and arginine residues in the haemolytic activity of SNTX. SNTX lost its haemolytic activity when the positively charged side chains of lysine residues were neutralized or converted into negatively charged side chains upon carbamylation or succinylation respectively. The haemolytic activity of SNTX was also inhibited by the modification of positively charged arginine residues using 2,3-butanedione. The loss of haemolysis showed strong correlation with the number of Lys or Arg residues modified. CD analyses, however, showed that the conformation of SNTX was not significantly affected by these chemical modifications. Further, the haemolytic activity of SNTX was competitively inhibited by various negatively charged lipids, such as phosphatidylserine, cardiolipin and monosialogangliosides. These results indicate that SNTX induces potent haemolytic activity through the formation of pores in the cell membrane, and that cationic residues play a crucial role in its cytolytic mechanism.

An in vitro pharmacological examination of venom from the soldierfish Gymnapistes marmoratus

The aim of the present study was to commence a characterisation of some of the basic pharmacological properties of venom from the soldierfish (Gymnapistes marmoratus). Soldierfish venom was prepared by extraction into 10% glycerol and centrifugation to remove insoluble material. Protein content was determined and venom concentrations were expressed as microgram venom protein. Soldierfish venom (0.5-15 micrograms/ml) produced concentration-dependent contractile responses in guinea-pig isolated ileum (GPI) and longitudinal smooth muscle (LSM) preparations. The muscarinic receptor antagonist atropine (10 nM) significantly inhibited responses of LSM to soldierfish venom (2.5 micrograms/ml). Responses to soldierfish venom (4-5 micrograms/ml) in GPI were not significantly affected by the ganglion-blocking drug mecamylamine (10 microM) or by incubation with blood cholinesterase. The cyclooxygenase inhibitor indomethacin (2 microM) significantly inhibited responses to soldierfish venom (2.5 micrograms/ml) in LSM. Neither the thromboxane A2/prostaglandin H2 receptor antagonist GR32191B (1 microM) nor the leukotriene receptor antagonist SB205312 (10 nM) significantly affected responses to soldierfish venom (5 micrograms/ml) in GPI. Responses to soldierfish venom (2.5-5 micrograms/ml) were not significantly inhibited by the histamine receptor antagonist mepyramine (0.5 microM), the angiotensin-converting enzyme inhibitor captopril (2 microM) or the neurokinin-1 receptor antagonist CP-99,994 (0.1 microM) in LSM. The angiotensin AT1 receptor antagonist EXP3174 (0.1 microM) also failed to inhibit significantly the responses to soldierfish venom (5 micrograms/ml) in GPI. A fluorometric assay for the detection of 5-hydroxytryptamine (5-HT) and related compounds indicated a level in soldierfish venom of 1.60 +/- 0.01 ng of 5-HT-like substance per microgram venom protein. Soldierfish venom (0.5-10 micrograms/ml) produced concentration-dependent contractile responses in rat isolated stomach fundus strips, and these responses (2.5 micrograms/ml) were significantly inhibited by the 5-HT1/5-HT2 receptor antagonist methysergide (0.1 microM). These results suggest that soldierfish venom may stimulate the release of acetylcholine to act at muscarinic receptors on guinea-pig gastrointestinal smooth muscle. The venom also appears to be causing the release of cyclooxygenase products, such as prostaglandins, and contains 5-HT, or a 5-HT-like substance, that acts directly at 5-HT receptors.

Stonustoxin is a novel lethal factor from stonefish (Synanceja horrida) venom. cDNA cloning and characterization

Stonustoxin (SNTX) is a multifunctional lethal protein isolated from venom elaborated by the stonefish, Synanceja horrida. It comprises two subunits, termed alpha and beta, which have respective molecular masses of 71 and 79 kDa. SNTX elicits an array of biological responses both in vitro and in vivo, particularly a potent hypotension that appears to be mediated by the nitric oxide pathway. As a prelude to structure-function studies, we have isolated and sequenced cDNA clones encoding the alpha- and beta-subunits of SNTX from a venom gland cDNA library. The deduced amino acid sequence of neither subunit shows significant homology with any known protein. Protein sequence alignment does, however, show the subunits to be 50% homologous to each other and implies that they may have arisen from a common ancestor. The subunits of this novel toxin lack typical N-terminal signal sequences commonly found in proteins that are secreted via the endoplasmic reticulum-Golgi apparatus pathway, indicating the possibility of its being secreted by a non-classical pathway, which is not clearly understood. The SNTX subunits have been expressed in Escherichia coli as cleavable fusion proteins that cross-react with antibodies raised against the native toxin. To the best of our knowledge, this is the first complete sequence of a fish-derived protein toxin to be reported.

Evidence for adrenergic and tachykinin activity in venom of the stonefish (Synanceja trachynis)

The aim of the present study was to investigate previously suggested adrenergic and tachykinin activity, as well as the cardiovascular effects, of venom from the stonefish (Synanceja trachynis). Stonefish venom (60-120 micrograms/kg, i.v.) produced dose-dependent bronchoconstriction in anaesthetised guinea-pigs. This response (100 micrograms/kg, i.v.) was significantly reduced by the neurokinin 1 (NK1) receptor antagonist CP-99,994 (1 mg/kg, i.v.). Contractile responses to venom (4 micrograms/ml) of guinea-pig isolated ileum (GPI) were significantly inhibited by a combination of the sodium channel blocking drug tetrodotoxin (1 microM) and the ganglion blocking drug mecamylamine (10 microM). However, subsequent administration of CP-99,994 (0.1 microM) did not produce further inhibition. Endogenous tachykinin depletion with capsaicin (1 microM) also significantly attenuated responses to venom (4 micrograms/ml) in GPI. Venom (4 micrograms/ml) produced increases in rate and force of contraction of rat spontaneously beating isolated atria which were significantly inhibited by the beta-adrenoceptor antagonist propranolol (5 microM) but not by noradrenergic transmitter depletion with reserpine (4.5 mg/kg, i.p.). In the presence of the alpha 1-adrenoceptor antagonist prazosin (0.3 microM), venom (6 micrograms/ml) significantly inhibited electrically evoked twitches of prostatic segments of rat vas deferens. The inhibitory effect of venom was significantly reduced by the alpha 2-adrenoceptor antagonist idazoxan (1 microM) but not by propranolol (5 microM) or the neurokinin 2 (NK2) receptor antagonist SR-48,968 (0.1 microM). Venom (60-120 micrograms/kg, i.v.) produced dose-dependent increases in mean arterial blood pressure in anaesthetised rats. This pressor response (60 micrograms/kg, i.v.) was significantly reduced by prazosin (10-50 micrograms/kg, i.v.) and the leukotriene receptor antagonist SB205312 (1 mg/kg, i.v.), significantly increased by propranolol (2 mg/kg, i.v.), but not significantly affected by the cyclo-oxygenase inhibitor indomethacin (10 mg/kg, i.v.) or the thromboxane A2/prostaglandin H2 (TP) receptor antagonist GR32191B (1 mg/kg, i.v.). Pressor responses to venom (100 micrograms/kg, i.v.) were also observed in anaesthetised rabbits. These results suggest that stonefish venom contains a component capable of stimulating the release of endogenous tachykinins with subsequent activity at NK1 receptors. The venom also appears to act via stimulation of sodium channels on sensory nerves. The venom also has activity at alpha 2-adrenoceptors and a direct action at beta-adrenoceptors. The effect of venom on blood pressure of anaesthetised rats appears to include a pressor component that is mediated, in part,by alpha-adrenoceptors and leukotriene receptors, and a depressor component that is mediated by beta-adrenoceptors. However, the pressor response does not involve action at TP receptors, or require the production of cyclo-oxygenase metabolites.

Pharmacological studies of stonefish (Synanceja trachynis) venom

The present study was designed to examine some of the pharmacological properties of venom from the stonefish (Synanceja trachynis), with particular reference to the presence in the venom of pain-producing/enhancing substances. Stonefish venom (1-6 micrograms/ml) produced concentration-dependent contractile responses in guinea-pig isolated ileum. No tachyphylaxis, or reduction in responses with time, was observed to venom (3 micrograms/ml) in ileum. The response to venom (3 micrograms/ml) was not significantly affected by the histamine antagonist mepyramine (0.5 microM), or a preceding anaphylactic response. Mecamylamine, 5HT-desensitization or EXP3174 failed to have any significant effect on responses to venom (3 micrograms/ml). Responses to venom (3 micrograms/ml) were significantly inhibited by the cyclooxygenase inhibitor indomethacin (5 microM), the leukotriene D4 receptor antagonist FLP55712 (1 microM), the thromboxane A2 receptor antagonist GR32191B (1 microM), the muscarinic receptor antagonist atropine (10 nM) and the neurokinin-1 receptor antagonist CP96345 (0.1 microM). Venom (6 micrograms/ml) produced contractile responses in the rat isolated vas deferens which were abolished by the alpha 1-adrenoceptor antagonist prazosin (0.3 microM) and significantly potentiated by the neuronal uptake inhibitor DMI (1 microM). However, noradrenergic transmitter depletion with reserpine (5 mg/kg, i.p.) did not significantly inhibit responses to venom (6 micrograms/ml). Histamine fluorometric and phospholipase A2 assays failed to detect significant quantities of either substance in the venom. These results suggest that stonefish venom may cause the release of acetylcholine, substance P, and cyclooxygenase products, or contain components which act at these receptors. The venom also appears to contain a component which is a substrate for neuronal uptake and has a direct action at alpha 1-adrenoceptors.

A review of stonefish venoms and toxins

Venoms from stonefish (genus Synanceja) have marked effects on the cardiovascular and neuromuscular systems and on vascular permeability; the venoms also exhibit haemolytic and hyaluronidase activity. Recently, a toxic protein, stonustoxin (SNTX), was purified from the venom of S. horrida: the primary lethal action of SNTX has been attributed to its potent endothelium-dependent vasorelaxant activity causing a rapid, marked and irreversible hypotension; the other actions of SNTX resemble those of the stonefish crude venoms.