Sarafotoxins and endothelins: evolution, structure and function

Distinct regulatory networks control toxin gene expression in elapid and viperid snakes

BACKGROUND

Venom systems are ideal models to study genetic regulatory mechanisms that underpin evolutionary novelty. Snake venom glands are thought to share a common origin, but there are major distinctions between venom toxins from the medically significant snake families Elapidae and Viperidae, and toxin gene regulatory investigations in elapid snakes have been limited. Here, we used high-throughput RNA-sequencing to profile gene expression and microRNAs between active (milked) and resting (unmilked) venom glands in an elapid (Eastern Brown Snake, Pseudonaja textilis), in addition to comparative genomics, to identify cis- and trans-acting regulation of venom production in an elapid in comparison to viperids (Crotalus viridis and C. tigris).

RESULTS

Although there is conservation in high-level mechanistic pathways regulating venom production (unfolded protein response, Notch signaling and cholesterol homeostasis), there are differences in the regulation of histone methylation enzymes, transcription factors, and microRNAs in venom glands from these two snake families. Histone methyltransferases and transcription factor (TF) specificity protein 1 (Sp1) were highly upregulated in the milked elapid venom gland in comparison to the viperids, whereas nuclear factor I (NFI) TFs were upregulated after viperid venom milking. Sp1 and NFI cis-regulatory elements were common to toxin gene promoter regions, but many unique elements were also present between elapid and viperid toxins. The presence of Sp1 binding sites across multiple elapid toxin gene promoter regions that have been experimentally determined to regulate expression, in addition to upregulation of Sp1 after venom milking, suggests this transcription factor is involved in elapid toxin expression. microRNA profiles were distinctive between milked and unmilked venom glands for both snake families, and microRNAs were predicted to target a diversity of toxin transcripts in the elapid P. textilis venom gland, but only snake venom metalloproteinase transcripts in the viperid C. viridis venom gland. These results suggest differences in toxin gene posttranscriptional regulation between the elapid P. textilis and viperid C. viridis.

CONCLUSIONS

Our comparative transcriptomic and genomic analyses between toxin genes and isoforms in elapid and viperid snakes suggests independent toxin regulation between these two snake families, demonstrating multiple different regulatory mechanisms underpin a venomous phenotype.

Crystal structure of human endothelin ETB receptor in complex with sarafotoxin S6b

Sarafotoxins (SRTXs) are endothelin-like peptides extracted from snake venom. SRTXs stimulate the endothelin ET_A and ET_B receptors and enhance vasoconstriction, followed by left ventricular dysfunction and bronchoconstriction. SRTXs include four major isopeptides, S6a-d, with different subtype selectivities. Here, we report the crystal structure of the human ET_B receptor in complex with the non-selective sarafotoxin S6b at 3.0 Å resolution. This structure reveals the similarities and differences between the binding modes of the endothelins and S6b. Moreover, molecular dynamics simulations based on the S6b-bound receptor provides structural insight into the subtype selectivity of the sarafotoxins. Our study clarifies the recognition mechanism of the endothelin-like peptide families.

A Comprehensive Multi-Omic Approach Reveals a Relatively Simple Venom in a Diet Generalist, the Northern Short-Tailed Shrew, Blarina brevicauda

Animals that use venom to feed on a wide diversity of prey may evolve a complex mixture of toxins to target a variety of physiological processes and prey-defense mechanisms. Blarina brevicauda, the northern short-tailed shrew, is one of few venomous mammals, and is also known to eat evolutionarily divergent prey. Despite their complex diet, earlier proteomic and transcriptomic studies of this shrew's venom have only identified two venom proteins. Here, we investigated with comprehensive molecular approaches whether B. brevicauda venom is more complex than previously understood. We generated de novo assemblies of a B. brevicauda genome and submaxillary-gland transcriptome, as well as sequenced the salivary proteome. Our findings show that B. brevicauda's venom composition is simple relative to their broad diet and is likely limited to seven proteins from six gene families. Additionally, we explored expression levels and rate of evolution of these venom genes and the origins of key duplications that led to toxin neofunctionalization. We also found three proteins that may be involved in endogenous self-defense. The possible synergism of the toxins suggests that vertebrate prey may be the main target of the venom. Further functional assays for all venom proteins on both vertebrate and invertebrate prey would provide further insight into the ecological relevance of venom in this species.

Toxinology provides multidirectional and multidimensional opportunities: A personal perspective

In nature, toxins have evolved as weapons to capture and subdue the prey or to counter predators or competitors. When they are inadvertently injected into humans, they cause symptoms ranging from mild discomfort to debilitation and death. Toxinology is the science of studying venoms and toxins that are produced by a wide variety of organisms. In the past, the structure, function and mechanisms of most abundant and/or most toxic components were characterized to understand and to develop strategies to neutralize their toxicity. With recent technical advances, we are able to evaluate and determine the toxin profiles using transcriptomes of venom glands and proteomes of tiny amounts of venom. Enormous amounts of data from these studies have opened tremendous opportunities in many directions of basic and applied research. The lower costs for profiling venoms will further fuel the expansion of toxin database, which in turn will provide greater exciting and bright opportunities in toxin research.

Mast cells and IgE in defense against lethality of venoms: Possible "benefit" of allergy[]

Physicians think of mast cells and IgE primarily in the context of allergic disorders, including fatal anaphylaxis. This 'bad side' of mast cells and IgE is so well accepted that it can be difficult to think of them in other contexts, particularly those in which they may have beneficial functions. However, there is evidence that mast cells and IgE, as well as basophils (circulating granulocytes whose functions partially overlap with those of mast cells), can contribute to host defense as components of adaptive type 2 immune responses to helminths, ticks and certain other parasites. Accordingly, allergies often are conceptualized as "misdirected" type 2 immune responses, in which IgE antibodies are produced against any of a diverse group of apparently harmless antigens, and against components of animal venoms. Indeed, certain unfortunate patients who have become sensitized to venoms develop severe IgE-associated allergic reactions, including fatal anaphylaxis, upon subsequent venom exposure. In this review, we will describe evidence that mast cells can enhance innate resistance, and survival, to challenge with reptile or arthropod venoms during a first exposure to such venoms. We also will discuss findings indicating that, in mice surviving an initial encounter with venom, acquired type 2 immune responses, IgE antibodies, the high affinity IgE receptor (FcεRI), and mast cells can contribute to acquired resistance to the lethal effects of both honeybee venom and Russell's viper venom. These findings support the hypothesis that mast cells and IgE can help protect the host against venoms and perhaps other noxious substances.

A nemertean excitatory peptide/CCHamide regulates ciliary swimming in the larvae of Lineus longissimus

Background

The trochozoan excitatory peptide (EP) and its ortholog, the arthropod CCHamide, are neuropeptides that are only investigated in very few animal species. Previous studies on different trochozoan species focused on their physiological effect in adult specimens, demonstrating a myo-excitatory effect, often on tissues of the digestive system. The function of EP in the planktonic larvae of trochozoans has not yet been studied.

Results

We surveyed transcriptomes from species of various spiralian (Orthonectida, Nemertea, Brachiopoda, Entoprocta, Rotifera) and ecdysozoan taxa (Tardigrada, Onychophora, Priapulida, Loricifera, Nematomorpha) to investigate the evolution of EPs/CCHamides in protostomes. We found that the EPs of several pilidiophoran nemerteans show a characteristic difference in their C-terminus. Deorphanization of a pilidiophoran EP receptor showed, that the two splice variants of the nemertean Lineus longissimus EP activate a single receptor. We investigated the expression of EP in L. longissimus larvae and juveniles with customized antibodies and found that EP positive nerves in larvae project from the apical organ to the ciliary band and that EP is expressed more broadly in juveniles in the neuropil and the prominent longitudinal nerve cords. While exposing juvenile L. longissimus specimens to synthetic excitatory peptides did not show any obvious effect, exposure of larvae to either of the two EPs increased the beat frequency of their locomotory cilia and shifted their vertical swimming distribution in a water column upwards.

Conclusion

Our results show that EP/CCHamide peptides are broadly conserved in protostomes. We show that the EP increases the ciliary beat frequency of L. longissimus larvae, which shifts their vertical distribution in a water column upwards. Endogenous EP may be released at the ciliary band from the projections of apical organ EP positive neurons to regulate ciliary beating. This locomotory function of EP in L. longissimus larvae stands in contrast to the repeated association of EP/CCHamides with its myo-excitatory effect in adult trochozoans and the general association with the digestive system in many protostomes.

Electronic supplementary material

The online version of this article (10.1186/s12983-019-0326-9) contains supplementary material, which is available to authorized users.

The Mast Cell-IgE Paradox: From Homeostasis to Anaphylaxis

Mast cells and IgE are so inextricably linked to the pathology of allergic disorders, including fatal anaphylaxis, that it can be difficult to think of them in other contexts. Surely, we do not have mast cells and IgE so that we can eat a peanut and die! It is thought that mast cells and IgE and basophils (circulating granulocytes, whose functions partially overlap with those of mast cells) can contribute to host defense as components of adaptive T helper cell type 2 immune responses to helminths, ticks, and certain other parasites. Accordingly, it was suggested that allergies are misdirected type 2 immune responses in which IgE antibodies are produced against any of a broad variety of apparently harmless antigens. However, components of animal venoms also can sensitize individuals to develop severe IgE-associated allergic reactions, including fatal anaphylaxis, on subsequent venom exposure. Here, I describe evidence that mast cells can enhance innate host resistance to reptile or arthropod venoms during responses to an initial exposure to such venoms and that acquired type 2 immune responses, IgE antibodies, the high-affinity IgE receptor FcεRI, and mast cells can contribute toward acquired resistance in mice to the lethal effects of honeybee or Russell's viper venom. These findings support the hypothesis that mast cells and IgE can help protect the host against noxious substances.

Mast cells and IgE in defense against venoms: Possible "good side" of allergy?

Physicians think of mast cells and IgE primarily in the context of allergic disorders, including fatal anaphylaxis. This 'bad side' of mast cells and IgE is so well accepted that it can be difficult to think of them in other contexts, particularly those in which they may have beneficial functions. However, there is evidence that mast cells and IgE, as well as basophils (circulating granulocytes whose functions partially overlap with those of mast cells), can contribute to host defense as components of adaptive type 2 immune responses to helminths, ticks and certain other parasites. Accordingly, allergies often are conceptualized as "misdirected" type 2 immune responses, in which IgE antibodies are produced against any of a diverse group of apparently harmless antigens, as well as against components of animal venoms. Indeed, certain unfortunate patients who have become sensitized to venoms develop severe IgE-associated allergic reactions, including fatal anaphylaxis, upon subsequent venom exposure. In this review, we will describe evidence that mast cells can enhance innate resistance to reptile or arthropod venoms during a first exposure to such venoms. We also will discuss findings indicating that, in mice which survive an initial encounter with venom, acquired type 2 immune responses, IgE antibodies, the high affinity IgE receptor (FcɛRI), and mast cells can contribute to acquired resistance to the lethal effects of both honeybee venom and Russell's viper venom. These findings support the hypothesis that mast cells and IgE can help protect the host against venoms and perhaps other noxious substances.

Ethnopharmacological survey of medicinal plants used by traditional healers and indigenous people in chittagong hill tracts, bangladesh, for the treatment of snakebite

Snakebites are common in tropical countries like Bangladesh where most snakebite victims dwell in rural areas. Among the management options after snakebite in Bangladesh, snake charmers (Ozha in Bengali language) are the first contact following a snakebite for more than 80% of the victims and they are treated mostly with the help of some medicinal plants. Our aim of the study is to compile plants used for the treatment of snakebite occurrence in Bangladesh. The field survey was carried out in a period of almost 3 years. Fieldwork was undertaken in Chittagong Hill Tracts, Bangladesh, including Chittagong, Rangamati, Bandarban, and Khagrachari. Open-ended and semistructured questionnaire was used to interview a total of 110 people including traditional healers and local people. A total of 116 plant species of 48 families were listed. Leaves were the most cited plant part used against snake venom. Most of the reported species were herb in nature and paste mostly used externally is the mode of preparation. The survey represents the preliminary information of certain medicinal plants having neutralizing effects against snake venoms, though further phytochemical investigation, validation, and clinical trials should be conducted before using these plants as an alternative to popular antivenom.

Atractaspis aterrima toxins: the first insight into the molecular evolution of venom in side-stabbers

Although snake venoms have been the subject of intense research, primarily because of their tremendous potential as a bioresource for design and development of therapeutic compounds, some specific groups of snakes, such as the genus Atractaspis, have been completely neglected. To date only limited number of toxins, such as sarafotoxins have been well characterized from this lineage. In order to investigate the molecular diversity of venom from Atractaspis aterrima—the slender burrowing asp, we utilized a high-throughput transcriptomic approach completed with an original bioinformatics analysis pipeline. Surprisingly, we found that Sarafotoxins do not constitute the major ingredient of the transcriptomic cocktail; rather a large number of previously well-characterized snake venom-components were identified. Notably, we recovered a large diversity of three-finger toxins (3FTxs), which were found to have evolved under the significant influence of positive selection. From the normalized and non-normalized transcriptome libraries, we were able to evaluate the relative abundance of the different toxin groups, uncover rare transcripts, and gain new insight into the transcriptomic machinery. In addition to previously characterized toxin families, we were able to detect numerous highly-transcribed compounds that possess all the key features of venom-components and may constitute new classes of toxins.

Endothelin antagonists in hypertension and kidney disease

The endothelin (ET) system seems to play a pivotal role in hypertension and in proteinuric kidney disease, including the micro- and macro-vascular complications of diabetes. Endothelin-1 (ET-1) is a multifunctional peptide that primarily acts as a potent vasoconstrictor with direct effects on systemic vasculature and the kidney. ET-1 and ET receptors are expressed in the vascular smooth muscle cells, endothelial cells, fibroblasts and macrophages in systemic vasculature and arterioles of the kidney, and are associated with collagen accumulation, inflammation, extracellular matrix remodeling, and renal fibrosis. Experimental evidence and recent clinical studies suggest that endothelin receptor blockade, in particular selective ETAR blockade, holds promise in the treatment of hypertension, proteinuria, and diabetes. Concomitant blockade of the ETB receptor is not usually beneficial and may lead to vasoconstriction and salt and water retention. The side-effect profile of ET receptor antagonists and relatively poor antagonist selectivity for ETA receptor are limitations that need to be addressed. This review will discuss what is currently known about the endothelin system, the role of ET-1 in the pathogenesis of hypertension and kidney disease, and summarize literature on the therapeutic potential of endothelin system antagonism.

Neurological effects of venomous bites and stings: snakes, spiders, and scorpions

Snake and spider bites, as well as scorpion sting envenoming, are neglected diseases affecting millions of people all over the world. Neurological complications vary according to the offending animal, and are often directly related to toxic effects of the venom, affecting the central nervous system, the neuromuscular transmission, the cardiovascular system, or the coagulation cascade. Snake bite envenoming may result in stroke or muscle paralysis. Metalloproteinases and other substances (common in vipers and colubrids) have anticoagulant or procoagulant activity, and may induce ischemic or hemorrhagic strokes. The venom of elapids is rich in neurotoxins affecting the neuromuscular transmission at either presynaptic or postsynaptic levels. The clinical picture of scorpion sting envenoming is dominated by muscle weakness associated with arterial hypertension, cardiac arrythmias, myocarditis, or pulmonary edema. These manifestations occur as the result of release of catecholamines into the bloodstream or due to direct cardiac toxicity of the venom. Cerebrovascular complications have been reported after the sting of the Indian red scorpion. Intracranial hemorrhages occur in the setting of acute increases in arterial blood pressure related to sympathetic overstimulation, and cerebral infarctions are related to either cerebral hypoperfusion, consumption coagulopathy, vasculitis, or cardiogenic brain embolism. Three main syndromes result from spider bite envenoming: latrodectism, loxoscelism, and funnel-web spider envenoming. Latrodectism is related to neurotoxins present in the venom of widow spiders. Most cases present with headache, lethargy, irritability, myalgia, tremor, fasciculation, or ataxia. Loxoscelism is caused by envenoming by spiders of the family Sicariidae. It may present with a stroke due to a severe coagulopathy. The venom of funnel-web spiders also has neurotoxins that stimulate neurotransmitter release, resulting in sensory disturbances and muscle paralysis. Proper management of the envenomed patient, including prompt transport to the hospital, correction of the hemostatic disorder, ventilatory support, and administration of antivenom, significantly reduce the risk of neurological complications which, in turn, reduce the mortality and improve the functional outcome of survivors.

Neurological complications of venomous snake bites: a review

Snake bite envenoming is a neglected tropical disease affecting millions of people living in the developing world. According to the offending snake species, the clinical picture may be dominated by swelling and soft tissue necrosis in the bitten limb, or by systemic or neurological manifestations. Serious neurological complications, including stroke and muscle paralysis, are related to the toxic effects of the venom, which contains a complex mixture of toxins affecting the coagulation cascade, the neuromuscular transmission, or both. Metalloproteinases, serine proteases, and C-type lentins (common in viper and colubrid venoms) have anticoagulant or procoagulant activity and may be either agonists or antagonists of platelet aggregation; as a result, ischemic or hemorrhagic strokes may occur. In contrast, the venom of elapids is rich in phospholipase A(2) and three-finger proteins, which are potent neurotoxins affecting the neuromuscular transmission at either presynaptic or post-synaptic levels. Presynaptic-acting neurotoxins (called β-neurotoxins) inhibit the release of acetylcholine, while post-synaptic-acting neurotoxins (called α-neurotoxins) cause a reversible blockage of acetylcholine receptors. Proper management of the envenomed patient, including prompt transport to the hospital, correction of the hemostatic disorder, ventilatory support, and administration of antivenom, significantly reduces the risk of neurological complications which, in turn, reduce the mortality and improve the functional outcome of survivors.

Pharmacological and structural characterization of long-sarafotoxins, a new family of endothelin-like peptides: Role of the C-terminus extension

Long-sarafotoxins (l-SRTXs) have recently been identified in both the venom of Atractaspis microlepidota and that of Atractaspis irregularis. They are characterized by different C-terminus extensions that follow the invariant Trp21, which plays a crucial role in endothelin-receptor binding. We initially determined the toxicity and three-dimensional structures of two chemically synthesized l-SRTXs that have different C-terminus extensions, namely SRTX-m (24 aa, including extension "D-E-P") and SRTX-i3 (25 aa, including extension "V-N-R-N"). Both peptides were shown to be highly toxic in mice and displayed the cysteine-stabilized α-helical motif that characterizes endothelins and short-SRTXs, to which a longer C-terminus with variable flexibility is added. To discern the functional and pharmacological consequences of the supplementary amino acids, different chimerical as well as truncated forms of SRTX were designed and synthesized. Thus, we either removed the extra-C-terminal residues of SRTX-m or i3, or grafted the latter onto the C-terminal extremity of a short-SRTX (s-SRTX) (ie. SRTX-b). Our competitive binding assays where SRTXs competed for iodinated endothelin-1 binding to cloned ET(A) and ET(B) receptor subtypes over-expressed in CHO cells, revealed the essential role of the C-terminus extensions for ET-receptor recognition. Indeed, l-SRTXs displayed an affinity three to four orders of magnitude lower as compared to SRTX-b for the two receptor subtypes. Moreover, grafting the C-terminus extension to SRTX-b induced a drastic decrease in affinity, while its removal (truncated l-SRTXs) yielded an affinity for ET-receptors similar to that of s-SRTXs. Furthermore, we established by intracellular Ca(2+) measurements that l-SRTXs, as well as s-SRTXs, display agonistic activities. We thus confirmed in these functional assays the major difference in potency for these two SRTX families as well as the crucial role of the C-terminus extension in their various pharmacological profiles. Finally, one of the chimeric toxin synthesized in this study appears to be one of the most potent and selective ligand of the ET(B) receptor known to date.

Potassium channel modulation by a toxin domain in matrix metalloprotease 23

Peptide toxins found in a wide array of venoms block K(+) channels, causing profound physiological and pathological effects. Here we describe the first functional K(+) channel-blocking toxin domain in a mammalian protein. MMP23 (matrix metalloprotease 23) contains a domain (MMP23(TxD)) that is evolutionarily related to peptide toxins from sea anemones. MMP23(TxD) shows close structural similarity to the sea anemone toxins BgK and ShK. Moreover, this domain blocks K(+) channels in the nanomolar to low micromolar range (Kv1.6 > Kv1.3 > Kv1.1 = Kv3.2 > Kv1.4, in decreasing order of potency) while sparing other K(+) channels (Kv1.2, Kv1.5, Kv1.7, and KCa3.1). Full-length MMP23 suppresses K(+) channels by co-localizing with and trapping MMP23(TxD)-sensitive channels in the ER. Our results provide clues to the structure and function of the vast family of proteins that contain domains related to sea anemone toxins. Evolutionary pressure to maintain a channel-modulatory function may contribute to the conservation of this domain throughout the plant and animal kingdoms.

Characteristics of neural and humoral systems involved in the regulation of blood pressure in snakes

Cardiovascular function is affected by many mechanisms, including the autonomic system, the kallikrein-kinin system (KKS), the renin-angiotensin system (RAS) and the endothelin system. The function of these systems seems to be fairly well preserved throughout the vertebrate scale, but evolution required several adaptations. Snakes are particularly interesting for studies related to the cardiovascular function because of their elongated shape, their wide variation in size and length, and because they had to adapt to extremely different habitats and gravitational influences. To keep the normal cardiovascular control the snakes developed anatomical and functional adaptations and interesting structural peculiarities are found in their autonomic, KKS, RAS and endothelin systems. Our laboratory has characterized some biochemical, pharmacological and physiological properties of these systems in South American snakes. This review compares the components and function of these systems in snakes and other vertebrates, and focuses on differences found in snakes, related with receptor or ligand structure and/or function in autonomic system, RAS and KKS, absence of components in KKS and the intriguing identity between a venom and a plasma component in the endothelin system.

The Endothelin/Sarafotoxin-Induced Increase of the Proliferation of Undifferentiated and DMSO-Differentiated GEM-81 Goldfish Erythrophoroma Cells is Mediated by ETB Receptors

Endothelins (ETs) and sarafotoxins (SRTXs) have been reported to exert ET(B)-mediated effects on vertebrate pigment cells. GEM-81 cell line, a red pigment cell-derived cutaneous tumor of the teleost Carassius auratus, expresses ET(B) receptors and can be differentiated with 1.5% DMSO treatment, thus constituting an useful model to investigate ET and SRTX effects on cultured fish pigment cells. Our aim was to characterize the pharmacology and biological effects mediated by ET receptors in DMSO-differentiated and undifferentiated cells. ET subtype receptors and their respective Ki values in both cell types were determined by competitive binding assays using (125)I ET-1 and BQ-485 (an ET(A) antagonist) or BQ-788 (an ET(B) antagonist). BQ-788, but not BQ-485, significantly reduced (125)I-ET-1 binding in both cell types, with similar low (Ki > nM) affinities. To determine the proliferation effects of ETs/SRTXs, cells were treated for 72 h with the hormones, and counted in a hemocytometer. The proliferation assays were repeated for SRTX S6c in the presence or absence of BQ-788. The results demonstrated that, with the exception of ET-1 (biphasic effect) and ET-3 (no significant effect) in undifferentiated GEM-81 cells, all the tested hormones induced increases in the proliferation of both types of cells. The hormones were equipotent in DMSO-differentiated cells, which exhibited increased sensitivity to ETs, but not to SRTXs, as compared with undifferentiated cells. The BQ-788 antagonistic effect was also exerted on the proliferation responses to SRTX S6c. These results corroborate the long and important evolutionary history of the ET/SRTX receptor system in vertebrate pigment cells.

Identification of crotasin, a crotamine-related gene of Crotalus durissus terrificus

Crotamine is a cationic peptide (4.9 kDa, pI 9.5) of South American rattlesnake, Crotalus durissus terrificus' venom. Its presence varies according to the subspecies or the geographical locality of a given species. At the genomic level, we observed the presence of 1.8 kb gene, Crt-p1, in crotamine-positive specimens and its absence in crotamine-negative ones. In this work, we described a crotamine-related 2.5 kb gene, crotasin (Cts-p2), isolated from crotamine-negative specimens. Reverse transcription coupled to polymerase chain reaction indicates that Cts-p2 is abundantly expressed in several snake tissues, but scarcely expressed in the venom gland. The genome of crotamine-positive specimen contains both Crt-p1 and Cts-p2 genes. The present data suggest that both crotamine and crotasin have evolved by duplication of a common ancestor gene, and the conservation of their three disulfide bonds indicates that they might adopt the same fold as beta-defensin. The physiological function of the crotasin is not yet known.

Long-sarafotoxins: characterization of a new family of endothelin-like peptides

Sarafotoxins (SRTXs) constitute a family of vasoactive peptides that were initially isolated from the venom of Atractaspis engaddensis, and that are structurally and functionally related to endothelins (ETs). Analysis of the venom of Atractaspis microlepidota microlepidota revealed several new SRTX molecules manifesting some new structural and functional characteristics. These novel SRTXs are longer by three amino acids than the previously described SRTXs, and are designated here "long-SRTXs". Six isoforms, derived from new poly-cistronic precursors, have been identified so far in the venom of this snake. One of these isoforms, designated SRTX-m, was chemically synthesized and its biological properties were studied. Our results show that SRTX-m induces toxicity in mice, mostly due to vasoconstriction, and also that it has a lower toxicity and potency than the more potent SRTX described up to now: sarafotoxin-b (SRTX-b) from A. engaddensis.

Expression and localization of endothelin receptors: implications for the involvement of peripheral glia in nociception

The endothelins (ETs) are peptides that have a diverse array of functions mediated by two receptor subtypes, the endothelin A receptor (ET(A)R) and the endothelin B receptor (ET(B)R). Pharmacological studies have suggested that in peripheral tissues, ET(A)R expression may play a role in signaling acute or neuropathic pain, whereas ET(B)R expression may be involved in the transmission of chronic inflammatory pain. To begin to define the mechanisms by which ET can drive nociceptive signaling, autoradiography and immunohistochemistry were used to examine the distribution of ET(A)R and ET(B)R in dorsal root ganglia (DRG) and peripheral nerve of the rat, rabbit, and monkey. In DRG and peripheral nerve, ET(A)R-immunoreactivity was present in a subset of small-sized peptidergic and nonpeptidergic sensory neurons and their axons and to a lesser extent in a subset of medium-sized sensory neurons. However, ET(B)R-immunoreactivity was not seen in DRG neurons or axons but rather in DRG satellite cells and nonmyelinating ensheathing Schwann cells. Thus, when ETs are released in peripheral tissues, they could act directly on ET(A)R-expressing sensory neurons and on ET(B)R-expressing DRG satellite cells or nonmyelinating Schwann cells. These data indicate that ETs can have direct, nociceptive effects on the peripheral sensory nervous system and that peripheral glia may be directly involved in signaling nociceptive events in peripheral tissues.

lynx1, an endogenous toxin-like modulator of nicotinic acetylcholine receptors in the mammalian CNS

Elapid snake venom neurotoxins exert their effects through high-affinity interactions with specific neurotransmitter receptors. A novel murine gene, lynx1, is highly expressed in the brain and contains the cysteine-rich motif characteristic of this class of neurotoxins. Primary sequence and gene structure analyses reveal an evolutionary relationship between lynx1 and the Ly-6/neurotoxin gene family. lynx1 is expressed in large projection neurons in the hippocampus, cortex, and cerebellum. In cerebellar neurons, lynx1 protein is localized to a specific subdomain including the soma and proximal dendrites. lynx1 binding to brain sections correlates with the distribution of nAChRs, and application of lynx1 to Xenopus oocytes expressing nAChRs results in an increase in acetylcholine-evoked macroscopic currents. These results identify lynx1 as a novel protein modulator for nAChRs in vitro, which could have important implications in the regulation of cholinergic function in vivo.

A snake bite by the Burrowing Asp, Atractaspis engaddensis

During routine milking of a group of Burrowing Asps Atractaspis engaddensis, one of the authors was bitten in the index finger by one fang, as is characteristic of bites by snakes of the genus. Local effects, oedema, erythema and numbness appeared within minutes, followed by systemic effects, including general weakness, sweating, pallor, fluctuations in the level of consciousness, vomiting and watery non-bloody diarrhoea. Gross oedema of the hand developed and extended up to the forearm. Two hours after admission to the hospital, blood pressure rose to 180/110, the ECG showed normal sinus rhythm and no signs of atrioventricular conduction block. An ECG obtained 24 h after the bite showed new T-wave inversions in leads V5 + 6, which gradually returned to baseline within several days. The local effects healed during the following weeks, but some discoloration and tenderness remained even 10 months after the bite. A maximal exercise (SPECT) study carried out five months after the bite was normal and a multigated radionuclear ventriculogram (MUGA) showed normal left-ventricular function. It may be assumed that the rise in blood pressure observed in this case reflects a systemic vasoconstrictive effect of the sarafotoxins, while the ST changes may have been caused by the direct effect of the toxins on the heart or indirectly by vasoconstriction of the coronary arteries. However, ischaemia secondary to a rise in blood pressure or to excitement could also explain the observed ECG-changes.

[Pathomorphology of coronary atherosclerosis]

The "American Heart Association Committee on Vascular Lesions" suggests the following morphologic classification of atherosclerotic plaques: the classification is based on large autopsy studies facilitating the assessment of the natural course of atherosclerotic lesions at precisely defined progression prone areas of the coronary tree from their clinically silent beginning to the stage where they produce symptoms. Lesion evolution is divided in 5 phases reflecting the possible time course of plaque development. Each phase is characterized by plaques with a distinctive morphology. The classification offers a framework of typical morphologies which the results of clinical investigations may be related to. Looking at the plaque composition, it is readily conceivable that atherosclerosis shares many characteristics with the general pathology of chronic inflammation and wound healing. Clinical symptoms e.g. acute coronary syndromes, arise from inflammation-mediated endothelial erosion and/or plaque rupture with ensuring coronary thrombosis. Advanced or complicated plaques are composed of different kinds of constituents in varying proportions. However, plaques at risk display a large lipid core occupying more than 40% of the plaque's volume, increased numbers of macrophages, reduced numbers of smooth muscle cells, an increased expression of tissue factor, and a thin plaque cap. Functionally, active plaques are characterized by a locally enhanced vasoreactivity with evidence coming from our own recent investigations that localised chronic inflammatory processes within the atherosclerotic plaque are responsible not only for the plaque rupture itself, but also for the hyperreactivity of these vessels to vasoconstrictor stimuli. In this context endothelin 1 (ET-1), a very potent vasoconstrictor peptide, may play an important role. ET-1 was originally reported to be produced by endothelial cells and to act locally in a paracrine fashion to regulate vascular tone. However, further studies have clarified that ET-1 is not only produced by endothelial cells but also by human inflammatory cells suggesting a role for ET-1 in inflammatory processes. Additionally, ET-1 displays a potent mitogenic activity. We examined immunohistochemically the presence of ET-1 in coronary plaque tissue obtained by directional coronary atherectomy. ET-1 immunoreactivity preferentially localized in plaque components indicative of a chronic inflammatory process. In addition, semiquantitative analysis of ET-1-like immunoreactivity revealed significantly higher staining grades in active coronary lesions compared with nonactive lesions. The increased ET-1 content in active coronary lesions may be beneficial to the stabilization of the vessel wall after plaque rupture and disadvantageous because it may lead to vasospasm and to the progression of atherosclerosis.

Resistance of the Egyptian mongoose to sarafotoxins

The Egyptian mongoose (Herpestes ichneumon) is known for its resistance to viperid and elapid venoms. The current work demonstrates that it is also resistant to the venom of Atractaspis and its most toxic component, sarafotoxin-b. Intravenous administration of this toxin, at a dose of about 13 times LD100 for mice, resulted in disturbance in electrocardiograms in the mongoose, which returned to normal after several hours. Sarafotoxin-b failed to induce contraction of mongoose aortal preparations. Endothelin-1, which was demonstrated in tissue extracts of the mongoose by immunological methods, induced contraction of the isolated mongoose aorta. This contraction, however, was greatly reduced when endothelin-1 was applied on top of sarafotoxin-b. Binding studies revealed endothelin/sarafotoxin-specific binding sites in brain and cardiovascular preparations of the mongoose. It is suggested that some structural features of endothelin/sarafotoxin receptors in the mongoose enable them to differentiate between the two peptides.

Evidence for a dual mechanism of gastric motor responses to intravenously administered endothelin-1 in anesthetized rats

We have recently reported that endothelin-1 (ET-1), administered intracisternally or microinjected into the DVC of rats, increases gastric motor function via vagal pathways. To determine whether circulating ET-1 acts peripherally or centrally to alter gastric motility, ET-1 (30 and 300 pmol/kg) was administered intravenously in alpha-chloralose anesthetized rats, while monitoring intragastric pressure, gastric motility, heart rate and blood pressure. Endothelin-1, at a dose of 300 pmol/kg, increased intragastric pressure, stimulated pyloric circular muscle contractile activity, and increased arterial pressure. When ET-1 (300 pmol/kg) was administered after bilateral vagotomy at midcervical level, a marked gastric motor inhibition with an increase in arterial blood pressure were observed. We conclude that the gastric motor effects of circulating ET-1 are a result of central excitatory and peripheral inhibitory actions of the peptide.

Identification of endothelin-1 in the pathophysiology of metastatic adenocarcinoma of the prostate

Prostate cancer is the second most common cause of death from cancer in U.S. men, and advanced, hormone-refractory disease is characterized by painful osteoblastic bone metastases. Endothelin-1, more commonly known as a potent vasoconstrictor, is a normal ejaculate protein that also stimulates osteoblasts. We show here that plasma immunoreactive endothelin concentrations are significantly elevated in men with metastatic prostate cancer and that every human prostate cancer cell line tested produces endothelin-1 messenger RNA and secretes immunoreactive endothelin. Exogenous endothelin-1 is a prostate cancer mitogen in vitro and increases alkaline phosphatase activity in new bone formation, indicating that ectopic endothelin-1 may be a mediator of the osteoblastic response of bone to metastatic prostate cancer.

Properties of Duvernoy's secretions from opisthoglyphous and aglyphous colubrid snakes

Relatively little attention has been given to the biological properties of Duvernoy's secretions produced by opisthoglyphous and some aglyphous colubrid snakes. A review is presented of literature pertaining to these secretions. Most detailed analyses of Duvernoy's secretions and their biological properties have been performed since the late 1970s. The dispholidines, Dispholidus typus and Thelotornis sp., and the natricines, Rhabdophis tigrinus and R. subminiata, have received the most attention due to the high toxicity of their secretions and their medical importance. These species produce secretions with variably strong prothrombin-activating activity, defibrinating activity, and hemorrhagic potential. Boigines, and natricines other than Rhabdophis, produce secretions of low to moderate toxicity and are variably hemorrhagic and proteolytic. Xenodontines and homalopsines similarly show hemorrhagic potential with low to moderate toxicity. Neurotoxic activity has been reported only from secretions of the boigines, Boiga blandingi and B. irregularis and the xenodontine, Heterodon platyrhinos. These species produce secretions containing postsynaptically acting components. Analyses of some of these secretions have shown that enzymes common to many ophidian venoms such as phospholipases A and L-amino acid oxidase are uncommon in the colubrid secretions studied. This may be due to few studies assaying for multiple enzyme activities and/or the unavailability of many secretion samples for study. Methods of secretion extraction, storage, and assay are discussed. Projected future research and the adaptive implications of Duvernoy's secretions are considered.

Biological activities of [Thr2]sarafotoxin-b, a synthetic analogue of sarafotoxin-b

The 21 amino acid sarafotoxins (SRTX) c and d/e as well as endothelin-3 (ET-3) are known to be less toxic and weaker pharmacologically than the other isopeptides SRTX-a, SRTX-b and ET-1. Since SRTX-c, SRTX-d/e and ET-3 possess a Thr instead of a Ser at position 2, we investigated the possibility that this mutation could be responsible for the observed biological differences. Here we show that the synthetic [Thr2]SRTX-b has indeed a lower vasoconstriction efficacy (approximately 35%) in the rabbit aorta, but it is nearly as potent as SRTX-b in toxicity tests and in influencing contraction of the rat uterus. Using monoclonal antibodies directed against the structurally related endothelin-1, we also show that the antigenicity of the analogue is comparable to that of SRTX-b, suggesting that the overall structure of the two peptides is similar, despite the substitution at position 2. We suggest that the Thr2 substitution contributes to the lower activity of the 'weak' peptides in some systems; however, additional substitutions found in the 'weak' peptides of the ET/SRTX family most probably contribute to their low pharmacological activity.