Neuroactive Toxins of Spider Venoms

Abstract

A variety of neuroactive toxins have been found in the venom of spiders. The venom of Latrodectus mactans(black widow spider) is known as a potent neurotoxin, fatal to humans and animals. The effective component, α-latrotoxin (Mr=130,000) acts on the nerve terminals, causing massive release of transmitters and depletion of the synaptic vesicles, by inducing influx of cations such as Ca²⁺and Na⁺through the channels existing in the presynaptic nerve terminals.

In the venom of Araneidspiders, a different type of toxin from the black widow spider venom was found. Joro spider toxin (JSTX) from Nephila clavat, NSTX from Nephila maculata, and argiopine (argiotoxin) from Argiope lobataact postsynaptically on glutamate receptors. These toxins share a common structure of a phenolic moiety connected to a polyamine. Chemical synthesis of these low molecular weight toxins has enabled morphological and biochemical studies of the glutamate receptors.

Recently, a third group of neurotoxins was found in genus Agelenidae. A number of toxins isolated from the venom of Agelenopsis aperta, Hololena curtaand Agelena opulentawere found to block synaptic transmission by a presynaptic mechanism. The structures of a number of Agelenidaetoxins have been characterized, and it has been shown that they block presynaptic calcium channels. These toxins should serve as useful tools for isolating and characterizing neuronal calcium channel proteins.     

Spider Polyamine Toxin

In the early 1980s, a new type of polyamine toxins was found in the venom of several orb-web spiders. Joro spider toxins (JSTXs) in the venom of Nephila clavata and Nephila spider toxins (NSTXs) derived from Nephila maculata blocked postsynaptic glutamate receptors in the invertebrate and vertebrate nervous system. Subsequently, chemical characterization and synthesis of JSTXs and NSTXs were carried out. These toxins and a synthetic analog, 1-naphthylacetylated spermine (Naspm), effectively suppressed glutamate channel responses of AMPA/KA type in mammalian central neurons. By use of recombinant subunit receptors expressed in Xenopus oocytes, JSTX was found to cause subunit specific block of the Ca²⁺-permeable AMPA receptors. This specific nature of JSTX was utilized to identify Ca²⁺-permeable AMPA receptors in various neurons and glial cells. The JSTXs strongly suppressed excitatory postsynaptic currents (EPSCs) in the hippocampal CA1 neurons after transient brain ischemia. The results indicate that JSTXs are effective at blocking abnormal EPSCs that may induce Ca²⁺ accumulation leading to delayed neuronal death after transient ischemic insult. Recent evidence shows that Ca²⁺-permeable AMPA receptors are involved in a variety of nervous diseases including amyotrophic lateral sclerosis (ALS) and allodynia. The JSTXs are potentially useful to understand pathogenesis of these diseases.     

Spider Neurotoxins as Tools for the Investigation of Glutamate Receptors

Abstract

Progress in the investigation of glutamate receptors structure and function requires the use of specific chemical tools affecting the responses to glutamate and other excitatory amino acids. Several low molecular weight spider and wasp toxins may be used as valuable tools for identification of certain subtypes of glutamate receptors and the study of their function. Some results obtained on different preparations with the help of argiotoxin 636 (argiopine), neurotoxin isolated from the venom Argiope lobata are reviewed in the present paper.     

Characterization of Glutamate Receptor by Spider Toxin

Abstract

Recent study has shown that the venom of some orb-web spiders contain potent blockers of the glutamate receptors. Joro spider toxin (JSTX) derived from Nephila clavata has been found to block excitatory postsynaptic potentials and glutamate-evoked responses in the neuromuscular synapse of crustacea, the squid giant synapse and the mammalian brain synapse. Structures of the toxins (JSTXs, NSTXs) of spiders belonging to the genus Nephila were determined and it was found that a unique 2,4-dihydroxyphenylacetyl asparaginyl cadaverine part was conserved between all toxins, indicating that this part is intimately involved in the blocking activity.

Labeling of synthesized JSTX-3 was used for histological investigation of glutamate receptors. Using autoradiography ¹²⁵I-JSTX-3 was found to bind at the lobster neuromuscular synapse. A histochemical study utilizing the interaction of biotinylated JSTX-3 with avidin showed specific binding of the toxin in rat hippocampus and cerebellum. JSTX-3 was used for isolation of glutamate receptors from brain. A crude synaptic membrane fraction from rat hippocampus and cerebellum was solubilized by Triton X-100. SDS-PAGE of the affinity purified JSTX-3 binding proteins showed at least 4 bands around 70 K daltons.     

Spider Neurotoxins Targeting Voltage-Gated Sodium Channels

The voltage-gated sodium (Na_v) channel is a target for a number of drugs, insecticides, and neurotoxins. These bind to at least seven identified neurotoxin binding sites and either block conductance or modulate sodium channel gating and/or kinetics. A number of polypeptide toxins from the venoms of araneomorph and mygalomorph spiders have been isolated and characterized that interact with several of these sites. Certain huwentoxins and hainantoxins appear to target site 1 to block Na_v channel conductance. The δ -atracotoxins and Magi 4 slow Na_v-channel inactivation via an interaction with neurotoxin site 3. The δ -palutoxins, and most likely μ -agatoxins and curtatoxins, target site 4. However, their action is complex with the μ -agatoxins causing a hyperpolarizing shift in the voltage-dependence of activation, an action analogous to scorpion β -toxins, but with both δ -palutoxins and μ -agatoxins slowing Na_v channel inactivation, a site 3-like action. Many spider toxins target undefined sites, while others are likely to cross-react with other ion channels due to conserved structures within domains of voltage-gated ion channels. It is already clear, however, that many spider toxins represent highly potent and specific molecular tools to define novel links between sites modulating channel activation and inactivation. Other spider toxins show phyla specificity and are being considered as lead compounds for the development of biopesticides. Others display tissue specificity via interactions with specific Na_v channel subtypes and should provide useful tools to delineate the molecular determinants to target ligands to these channel subtypes. These studies are being greatly assisted by the determination of the pharmacophore of these toxins, but without precise identification of their binding site and mode of action their potential in the mentioned areas remains underdeveloped.     

蛇毒毒素的抗肿瘤作用及其在医药领域的应用

目的 探讨蛇毒毒素的抗肿瘤作用及其在医药领域的应用。方法 综述蛇毒毒素的抗肿瘤组分、抗肿瘤作用及其机制的研究进展。结果 蛇毒毒素对多种肿瘤均有抑制作用,具有直接杀伤肿瘤细胞、诱导肿瘤细胞凋亡、抑制血管再生等作用。结论 对蛇毒毒素抗肿瘤组分及其作用机制进行深入研究,是当前抗肿瘤药物研究的重要方向。     

Cellular Models in Natural Toxins Investigations: Intestinal and Kidney Cell Lines

Abstract

Cell cultures are increasingly used in toxicology. Cell lines, also of human origin are available, which have been widely studied for their capability of expressing in vitro the specialized functions of the tissues of origin.

When intestinal and renal cell lines are cultured on inserts, it is possible to study the effects of toxicants on epithelial barriers with regard to cell injury, transport and apical or basolateral cellular exposure.

This review describes natural toxins studies performed with the human intestinal adenocarcinoma cell lines Caco-2, HT-29, T84 and with the renal cell lines MDCK (canine) and LLC-PK1 (porcine).

These studies represent an interesting and fairly new approach in the field of natural toxins dealing with in vitro target-organ experimental models.     

An Overview of The Three Dimensional Structure of Short Spider Toxins

Arthropods are one of the most diverse animal groups on the Earth. Spiders belong to this phylum and they are ancient animals with a history going back some three hundred million years. They are abundant, widespread, and natural controllers of insect populations. They use their venom to capture prey or to fight against predators. This venom is constituted of various peptides and enzymes with different activities. Among these proteins, toxic peptides are responsible for the macroscopic effect of the venom.

Most of the toxins are known to interact with ion channels (mainly potassium channels, sodium channels, and calcium channels). These transmembrane molecules are ubiquitous in the cells. They underlie a broad range of the most basic biological processes, from excitation and signaling to secretion and absorption. Like enzymes they are diverse and ubiquitous macromolecular catalysts with high substrate specificity and subject to strong regulation. Animal toxins and, more specifically, spider toxins are effectors of these channels. Depending on the peptide, they have ability to block the channel by plugging into its pore of conduction, or by modifying the opening and closing capacity of the channels, binding on a few specific sites along the structure of the channel.

Most of these peptides fold according to the overall same pattern, the inhibitor cystine knot (ICK) scaffold. Basically, it consists of a ring formed by a part of the backbone of the peptide and two disulfide bridges, penetrated by a third disulfide bridge. An additional disulfide bridge might be found in some toxins. Another fold has been found in a few toxins and has been described as the DDH scaffold. This motif lacks the knot and comprises an antiparallel β -hairpin stabilized by two conserved disulfide bridges.

This paper will try to summarize the structural characteristics of the spider toxins for which the fold has been described in the literature.     

Precious Natural Peptides from Spider Venoms: New Tools for Studying Potassium Channels

Among the large variety of animal toxins that target potassium channels, spider peptides constitute an unique class of voltage-dependent K⁺ (Kv) current inhibitors according to their structure and pharmacological properties. Spider toxins that block Kv currents are small basic peptides the include three disuflide bridges and belong to the family of inhibitor cystine knot (ICK) molecules. Unlike snake, bee, scorpion, or sea anemone toxins that block Kv1 or Kv3 channels, ICK spider toxins target Kv2 and Kv4 channels, which are expressed in the central nervous system (CNS) and in the cardiovascular system. Their selective affinities for Kv2 and/or Kv4 subfamilies are very useful for dissecting these currents in neuronal and cardiac cells and for the determination of their contribution in physiological processes. Their mode of action is also original, since they induce a shift of channel opening to more depolarized potentials that alter the voltage-dependent properties of K currents. Then they are called gating modifiers. Structure-function studies of these gating modifiers were recently facilitated by solving their tridimensional structure together with the crystallization of prokaryotic K⁺ channels. Spider toxins present an active molecular surface, including a hydrophobic patch surrounded by charged residues, which are important for their binding on Kv channels. Gating modifiers interact with important residues in the S3C-S4 external loop via both hydrophobic and electrostatic interactions. Several dynamic interaction models were proposed, but all of them remain putative.     

The potential use of toxin antibodies as a strategy for controlling acute Staphylococcus aureus infections

Introduction: The pandemic human pathogen, Staphylococcus aureus, displays high levels of antibiotic resistance and is a major cause of hospital- and community-associated infections. S. aureus disease manifestation is to a great extent due to the production of a large arsenal of virulence factors, which include a series of secreted toxins. Antibodies to S. aureus toxins are found in people who are infected or asymptomatically colonized with S. aureus. Immunotherapies consisting of neutralizing anti-toxin antibodies could provide immediate aid to patients with impaired immune systems or in advanced stages of disease.

Areas covered: Important S. aureus toxins, their roles in pathogenesis, rationales for selecting S. aureus toxins for immunization efforts, and caveats associated with monoclonal antibody-based passive immunization are discussed. This review will focus on hyper-virulent community-associated methicillin-resistant S. aureus because of their recent surge and clinical importance.

Expert opinion: Antibodies against genome-encoded toxins may be more broadly applicable than those directed against toxins found only in a sub-population of S. aureus isolates. Furthermore, there is substantial functional redundancy among S. aureus toxins. Thus, an optimal anti-S. aureus formulation may consist of multiple antibodies directed against a series of key S. aureus genome-encoded toxins.     

Recent Advances in Research on Widow Spider Venoms and Toxins

Widow spiders have received much attention due to the frequently reported human and animal injures caused by them. Elucidation of the molecular composition and action mechanism of the venoms and toxins has vast implications in the treatment of latrodectism and in the neurobiology and pharmaceutical research. In recent years, the studies of the widow spider venoms and the venom toxins, particularly the α-latrotoxin, have achieved many new advances; however, the mechanism of action of the venom toxins has not been completely clear. The widow spider is different from many other venomous animals in that it has toxic components not only in the venom glands but also in other parts of the adult spider body, newborn spiderlings, and even the eggs. More recently, the molecular basis for the toxicity outside the venom glands has been systematically investigated, with four proteinaceous toxic components being purified and preliminarily characterized, which has expanded our understanding of the widow spider toxins. This review presents a glance at the recent advances in the study on the venoms and toxins from the Latrodectus species.     

Cobra (Naja Naja Atra) Membrane Toxin Isoforms: Structure and Function

Abstract

Two membrane toxins, termed MT-I and MT-II, were purified to HPLC homogeneity from the venom of Naja naja atra. The NH₂-terminal sequences of the two isoforms were determined. When compared with the known sequences of membrane toxins, we concluded they are CTX-I and CTX-III (from Naja naja atra), respectively. Membrane toxins are basic peptides typified by a chain of 60 amino acids long. Their pi is about 10 and Mr is 6,000-7,000. About half of the amino acids are hydrophobic.

There is lytic synergism between membrane toxins and phospholipase A₂. Membrane toxins, which are different from neurotoxins, are capable of depolarizing muscle cells. The toxins are able to kill cancer cells in vitro. Electrocardiograph of cat to which membrane toxin was applied shows magnificent changes. A positive correlation exists between hydrophobicities and activities of the toxins to inhibit protein kinase C (PKC) activity. All the effects are the result of action of the toxins on cell membranes. In addition, structure-activity relationships are investigated with the available comparative data for membrane toxins centering on LD₅₀, erythrocyte lysis, and muscle cell depolarization.     

Reverse Biology Applied to Micrurus corallinus,a South American Coral Snake

Abstract

Little is known about the coral snakes venom components. Clarification of the primary structure of polypeptidic toxins was hampered until now by the lack of enough venom for protein purification and chemistry. Using the Reverse Biology approach, several potential Micrurus corallinus toxins were characterized by cDNA cloning. The deduced proteins shared homology with known snake toxins, such as α-neurotoxins, phospholipase A₂, natriuretic peptides and lectins. To our knowledge, these are the first complete primary structure characterization of coral snake venom toxins.     

Acetylcholinesterase inhibitors: a patent review (2008 – present)

Introduction: Both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are present in the body in large amounts. AChE is an important part of the cholinergic nervous system taking place in the central and peripheral nervous system. AChE is a target of several toxins such as insecticide carbofuran, nerve agents, sarin, soman, tabun and VX. Beside toxins, drugs for treatment of Alzheimer's disease and myasthenia gravis, such as galantamine, donepezil, rivastigmine, tacrine, huperzine, pyridostigmine and neostigmine, are known.

Areas covered: The review gives an overview of the importance of the cholinergic nervous system, the biochemistry of AChE and the role of AChE inhibitors. Current efforts to introduce potent drugs for Alzheimer's disease therapy and reduce toxicity, while keeping the maximal pharmacological effect, are also discussed.

Expert opinion: The current research effort into AChE inhibitors can be divided into two categories. First, new toxins useful for agricultural purposes and second, novel drugs that need to be prepared, although there is less interest in the new toxins. The research for drugs for Alzheimer's disease needs to focus on inhibitors that reduce the deposition of amyloid plaques, but do not initiate AChE expression.     

Natural Toxins in Thailand

Abstract

Natural toxins are one of the national health problems of Thailand that is often overlooked. Based on the available data from reported cases with clinical relevance, animal toxins constitute 98 per cent, and plant toxins comprise only 2 per cent. Among the animal toxin poisoning poisonous snake envenomation forms the imajority of the problem with some sporadic reports of poisoning from insect and marine toxins. In general, scientific interest in toxinology is still few. There is growing attention to the area of pathophysiology of snake envenomation with respect to hemodynamics and organ pathology. Marine toxins and plant toxins begin to attract more scientific interest.     

Microbiota-derived uremic retention solutes: perpetrators of altered nonrenal drug clearance in kidney disease

Introduction: Scientific interest in the gut microbiota is increasing due to improved understanding of its implications in human health and disease. In patients with kidney disease, gut microbiota-derived uremic toxins directly contribute to altered nonrenal drug clearance. Microbial imbalances, known as dysbiosis, potentially increase formation of microbiota-derived toxins, and diminished renal clearance leads to toxin accumulation. High concentrations of microbiota-derived toxins such as indoxyl sulfate and p-cresol sulfate perpetrate interactions with drug metabolizing enzymes and transporters, which provides a mechanistic link between increases in drug-related adverse events and dysbiosis in kidney disease.

Areas covered: This review summarizes the effects of microbiota-derived uremic toxins on hepatic phase I and phase II drug metabolizing enzymes and drug transporters. Research articles that tested individual toxins were included. Therapeutic strategies to target microbial toxins are also discussed.

Expert commentary: Large interindividual variability in toxin concentrations may explain some differences in nonrenal clearance of medications. Advances in human microbiome research provide unique opportunities to systematically evaluate the impact of individual and combined microbial toxins on drug metabolism and transport, and to explore microbiota-derived uremic toxins as potential therapeutic targets.     

Sphingosine Analogs: an Emerging New Class of Toxins that Includes the Fumonisins

Abstract

There is an emerging new class of toxins - the sphingosine analog toxins. First to be identified were the AAL toxins, host-specific toxins produced by the fungus Alternaria alternata f. sp. lycopersici to facilitate invasion of tissues in susceptible plants. The best studied members of the class are the fumonisins, which were initially isolated as tumor promoters from corn infested with Fusarium moniliforme, the major ear rot fungus of corn and an important pathogen of stored grains worldwide. Recently, the sphingosine analog toxins penaresidins A and B and penazetidine A have been isolated from marine sponges of the Penares genus. All these toxins are long-chain fatty amines with free amino groups. The mycotoxins are characterized by the absence of a C-1 hydroxyl group and the presence of one or more propanetricarboxylic acid esters, whereas the sponge toxins are characterized by a four-membered azetidine ring. The observation that removing propanetricarboxylic acid moieties from fumonisins by alkaline hydrolysis yields fragments that have half the molecular weight but retain comparable cytotoxic activity over a broader spectrum of mammalian cell lines has prompted the suggestion that metabolism by non-specific carboxylesterases may be a required initial step in their toxic mechanism. Toxins in this new class presumably act as either agonists, antagonists or synthesis inhibitors of sphingosine, which is becoming recognized as an important intracellular regulatory molecule. These toxins may prove useful as experimental tools to explore the regulatory roles of sphingosine.     

Natural Protein Toxins Affecting Cutaneous Microvascular Permeability

Abstract

Natural toxins are found widespread from animal, plant and micro-organism sources. Presented here in review are recently discovered natural protein toxins that have in some way been shown to affect the permeability of the cutaneous micro-vasculature or skin capillaries.

Capillaries play a major role in the body by controlling the necessary normal balance of metabolites in the body's tissues and that of the blood. The trans-capillary exchanges of water and metabolites are regulated by the basal lamina, the internal activities of the endothelial cells and the driving forces on each side of the capillary wall. Edema, inflammation, urticaria, increased capillary permeability and cutaneous edema are conditions that are related. The main methods for detecting the increase in skin capillary permeability have been by using the rat paw edema assay, labelled albumin, or other detectable indicators.

Natural venoms and toxins sources causing edema include mammals, reptiles, amphibians, fishes, invertebrates, plants, and micro-organisms. Not all the substances causing increased capillary permeability are proteins such as certain alkaloids (Plants, fungi, fire ants and others) and normal endogenous substances e.g. histamine, serotonin, acetylcholine, (plants, snakes, and others) and are not considered in this review.

Recently, a large number of toxins (predominantly bacterial toxins) have been reported that produce increased cutaneous capillary permeability, some of which are known in some detail and selected toxins are discussed.

These studies have helped to understand the toxins, provided for more effective treatments, and helped to improve our knowledge of the capillaries and endothelial cells.