Cardiovascular studies on venom from the soldierfish (Gymnapistes marmoratus)

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.

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.

Cardiovascular effects of Sp-CTx, a cytolysin from the scorpionfish (Scorpaena plumieri) venom

Fish venom cytolysins are multifunctional proteins that in addition to their cytolytic/hemolytic effects display neurotoxic, cardiotoxic and inflammatory activities, being described as "protein lethal factors". A pore-forming cytolysin called Sp-CTx (Scorpaena plumieriCytolytic Toxin) has been recently purified from the venom of the scorpionfish Scorpaena plumieri. It is a glycoprotein with dimeric constitution, comprising subunits of approximately 65 kDa. Previous studies have revealed that this toxin has a vasorelaxant activity that appears to involve the L-arginine-nitric oxide synthase pathway; however its cardiovascular effects have not been fully comprehended. The present study examined the cardiovascular effects of Sp-CTx in vivo and in vitro. In anesthetized rats Sp-CTx (70 μg/kg i.v) produced a biphasic response which consisted of an initial systolic and diastolic pressure increase followed by a sustained decrease of these parameters and the heart rate. In isolated rats hearts Sp-CTx (10(-9) to 5 × 10(-6) M) produced concentration-dependent and transient ventricular positive inotropic effect and vasoconstriction response on coronary bed. In papillary muscle, Sp-CTx (10(-7) M) also produced an increase in contractile isometric force, which was attenuated by the catecholamine releasing agent tyramine (100 μM) and the β-adrenergic antagonist propranolol (10 μM). On isolated ventricular cardiomyocytes Sp-CTx (1 nM) increased the L-type Ca(2+) current density. The results show that Sp-CTx induces disorders in the cardiovascular system through increase of sarcolemmal calcium influx, which in turn is partially caused by the release of endogenous noradrenaline.

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.

Hypotensive Effects of the Crotalus Durissus Cascavella Venom: Involvement of NO

Crotalus durissus cascavella is a snake native of northeastern Brazil. The aim of the study was to investigate the effects of C. d. cascavella venom on rat mean arterial pressure and vascular reactivity in the mesenteric vascular bed. The venom evoked a dose-dependent decrease in mean arterial pressure, cardiac and respiratory frequency with increased plasma nitrite levels. L-NAME (10 mg/kg) blunted both the hypotension and increased nitrite production observed after the venom administration. To investigate the effects of C. d. cascavella in resistance vessels, the vascular mesenteric bed was studied, and the results suggested that the hypotensive effect of the venom is not dependent on a direct vasodilatory activity. In conclusion, C. d. cascavella venom presented indirect hypotensive effects with the involvement of nitric oxide.

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.

Cardiovascular effects of scorpionfish (Scorpaena plumieri) venom

The aim of the present study was to investigate the cardiovascular activity of Scorpaena plumieri venom in both in vivo and in vitro models. In anesthetized rats, doses of the venom (14-216 microg protein/kg) induced a transient increase in the mean arterial pressure. However at higher dose (338 microg protein/kg) this effect was followed by a sudden hypotension and the animal evolved to death. The heart rate was temporarily increased and followed by bradycardia using doses > or =108 microg/kg. In isolated rat hearts the crude venom (5-80 microg protein) produced dose-dependent positive ventricular chronotropic, inotropic, lusitropic and coronary vasoconstriction responses. Partial purification of an active fraction (CF, cardiovascular fraction) which reproduced the cardiovascular effects induced by crude venom on isolated hearts was achieved by conventional gel filtration chromatography. Adrenergic blockades, prazosin and propranolol, significantly attenuated these responses. The coronary vasoconstriction response to CF was also attenuated by chemical endothelium denudation. In conclusion, the data showed that S. plumieri fish venom induces disorders in the cardiovascular system. It also suggests that alpha(1) and beta-adrenergic receptors, and the vascular endothelium, are involved at least partially, in these cardiac effects.

Phylogenesis of constitutively formed nitric oxide in non-mammals

It is widely recognized that nitric oxide (NO) in mammalian tissues is produced from L-arginine via catalysis by NO synthase (NOS) isoforms such as neuronal NOS (nNOS) and endothelial NOS (eNOS) that are constitutively expressed mainly in the central and peripheral nervous system and vascular endothelial cells, respectively. This review concentrates only on these constitutive NOS (cNOS) isoforms while excluding information about iNOS, which is induced mainly in macrophages upon stimulation by cytokines and polysaccharides. The NO signaling pathway plays a crucial role in the functional regulation of mammalian tissues and organs. Evidence has also been accumulated for the role of NO in invertebrates and non-mammalian vertebrates. Expression of nNOS in the brain and peripheral nervous system is widely determined by staining with NADPH (reduced nicotinamide adenine dinucleotide phosphate) diaphorase or NOS immunoreactivity, and functional roles of NO formed by nNOS are evidenced in the early phylogenetic stages (invertebrates and fishes). On the other hand, the endothelium mainly produces vasodilating prostanoids rather than NO or does not liberate endothelium-derived relaxing factor (EDRF) (fishes), and the ability of endothelial cells to liberate NO is observed later in phylogenetic stages (amphibians). This review article summarizes various types of interesting information obtained from lower organisms (invertebrates, fishes, amphibians, reptiles, and birds) about the properties and distribution of nNOS and eNOS and also the roles of NO produced by the cNOS as an important intercellular signaling molecule.

Modulation of intracellular Ca2+ levels by Scorpaenidae venoms

The crude venoms of the soldierfish (Gymnapistes marmoratus), the lionfish (Pterois volitans) and the stonefish (Synanceia trachynis) display pronounced neuromuscular activity. Since [Ca(2+)](i) is a key regulator in many aspects of neuromuscular function we sought to determine its involvement in the neuromuscular actions of the venoms. In the chick biventer cervicis muscle, all three venoms produced a sustained contraction (approx 20-30% of 1mM acetylcholine). Blockade of nicotinic receptors with tubocurarine (10 micro M) failed to attenuate the contractile response to either G. marmoratus venom or P. volitans venom, but produced slight inhibition of the response to S. trachynis venom. All three venoms produced a rise in intracellular Ca(2+) (approx. 200-300% of basal) in cultured murine cortical neurons. The Ca(2+)-channel blockers omega-conotoxin MVIIC, omega-conotoxin GVIA, omega-agatoxin IVa and nifedipine (each at 1 micro M) potentiated the increase in [Ca(2+)](i) in response to G. marmoratus venom and P. volitans venom, while attenuating the response to S. trachynis venom. Removal of extracellular Ca(2+), replacement of Ca(2+) with La(3+) (0.5mM), or addition of stonefish antivenom (3units/ml) inhibited both the venom-induced increase in [Ca(2+)](i) in cultured neurones and contraction in chick biventer cervicis muscle. Venom-induced increases in [Ca(2+)](i) correlated with an increased cell death of cultured neurones as measured using propidium iodide (1 micro g/ml). Morphological analysis revealed cellular swelling and neurite loss consistent with necrosis. These data indicate that the effects of all three venoms are due in part to an increase in intracellular Ca(2+), possibly via the formation of pores in the cellular membrane which, under certain conditions, can lead to necrosis.

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.

Adrenergic and cholinergic activity contributes to the cardiovascular effects of lionfish (Pterois volitans) venom

The aim of the present study was to further investigate the cardiovascular activity of Pterois volitans crude venom. Venom (0.6-18 microg protein/ml) produced dose- and endothelium-dependent relaxation in porcine coronary arteries that was potentiated by atropine (10nM), but significantly attenuated by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (NOLA; 0.1mM), by prior exposure of the tissue to stonefish antivenom (SFAV, 3 units/ml, 10 min), or by removal of extracellular Ca(2+). In rat paced left atria, venom (10 microg protein/ml) produced a decrease, followed by an increase, in contractile force. Atropine (0.5 microM) abolished the decrease in force and potentiated the increase. Propranolol (5 microM) did not affect the decrease in force but significantly attenuated the increase. In spontaneously beating right atria, venom (10 microg protein/ml) produced an increase in rate that was significantly attenuated by propranolol (5 microM). Prior incubation with SFAV (0.3 units/microg protein, 10 min) abolished both the inotropic and chronotropic responses to venom. In the anaesthetised rat, venom (100 micro protein/kg, i.v.) produced a pressor response, followed by a sustained depressor response. Atropine (1mg/kg, i.v.) potentiated the pressor response. The further addition of prazosin (50 microg/kg, i.v.) restored the original response to venom. Prior administration of SFAV (100 units/kg, i.v., 10 min) significantly attenuated the in vivo response to venom. It is concluded that P. volitans venom produces its cardiovascular effects primarily by acting on muscarinic cholinergic receptors and adrenoceptors. As SFAV neutralised many of the effects of P. volitans venom, we suggest that the two venoms share a similar component(s).

Stonefish (Synanceia spp.) antivenom neutralises the in vitro and in vivo cardiovascular activity of soldierfish (Gymnapistes marmoratus) venom

The soldierfish (Gymnapistes marmoratus), which is related to the stonefish (Synanceia spp.), inhabits the western, southern and lower eastern coastlines of Australia. We have previously found that G. marmoratus venom possesses pharmacological activity similar to Synanceia trachynis venom (Hopkins, B.J., Hodgson, W.C., 1998. Cardiovascular studies on venom from the soldierfish (Gymnapistes marmoratus). Toxicon 36, 973-872; Church, J.E., Hodgson, W.C., 2000. Dose-dependent cardiovascular and neuromuscular effects of stonefish (Synanceja trachynis) venom. Toxicon 38, 391-407), namely an action at muscarinic receptors and adrenoceptors. The aim of this study was to determine the effectiveness of Synanceia antivenom in neutralising the in vitro and in vivo cardiovascular activity of G. marmoratus venom. Venom extract (0.4-12 microg protein/ml) caused dose- and endothelium-dependent relaxation in porcine U46619-precontracted coronary arteries. This relaxation was abolished by 10 min prior exposure of the tissue to Synanceia antivenom (3 units/ml). In rat paced (5 ms, 2 Hz, 7-12 V) left atria, G. marmoratus venom extract (40 microg protein/ml) produced a transient negative, followed by a sustained positive inotropic response. In spontaneously beating right atria, venom extract (40 microg protein/ml) produced similar changes in rate. Prior incubation of venom extract with Synanceia antivenom (1 unit/4 microg venom extract protein, 10 min) significantly attenuated both components of the inotropic response, and abolished the positive chronotropic response. In the anaesthetised rat, venom extract (400 microg protein/kg, i.v.) produced a transient depressor response, followed by a more sustained pressor response. Prior incubation of venom extract with Synanceia antivenom (1 unit/4 microg venom extract protein, 10 min) significantly attenuated both components of the in vivo response. As Synanceia antivenom neutralised the cardiovascular activity of G. marmoratus venom both in vitro and in vivo, we suggest that the venoms of the two species may share a similar component(s).