Names | |
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IUPAC name | |
Other names 1H,10H-Pyrrolo(1,2-c)purine-10,10-diol, 2-amino-4-(((aminocarbonyl)oxy)methyl)-3a,4,5,6,8,9-hexahydro-5-hydroxy-6-imino-, (3aS,4R,10aS)-; 1H,10H-Pyrrolo(1,2-c)purine-10,10-diol, 2-amino-4-((aminocarbonyl)oxy)methyl-3a,4,5,6,8,9-hexahydro-5-hydroxy-6-imino-,(3aS,4R,10aS)-; 1H,10H-Pyrrolo(1,2-c)purine-10,10-diol, 2-amino-4-((aminocarbonyl)oxy)methyl-3a,4,5,6,8,9-hexahydro-5-hydroxy-6-imino-,(3aS-(3aalpha,4alpha,10aR*))- | |
Identifiers | |
3D model (JSmol) | |
ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.237.662 |
KEGG | |
PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
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Properties | |
C10H17N7O5 | |
Molar mass | 315.286 |
Hazards | |
GHS labelling: | |
Danger | |
H300 | |
P264, P270, P301+P310, P321, P330, P405, P501 | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Neosaxitoxin (NSTX) is included, as other saxitoxin-analogs, in a broad group of natural neurotoxic alkaloids, commonly known as the paralytic shellfish toxins (PSTs). The parent compound of PSTs, saxitoxin (STX), is a tricyclic perhydropurine alkaloid, which can be substituted at various positions, leading to more than 30 naturally occurring STX analogues. All of them are related imidazoline guanidinium derivatives. [3]
NSTX, and other PSTs, are produced by several species of marine dinoflagellates (eukaryotes) and freshwater cyanobacteria, blue-green algae (prokaryotes), which can form extensive blooms around the world. [4] Under special conditions, during harmful algal blooms (HAB) or red tide, all these toxins may build up in filter-feeding shellfish, such as mussels, clams and oysters, and can produce an outbreak of Paralytic Shellfish Poisoning (PSP). [5]
Saxitoxin analogues associated to PSP can be divided into three categories: [6]
NSTX is quite similar to saxitoxin, like all the neurotoxins associated to PSP, the only difference is that NSTX shows one hydroxyl group bonded to nitrogen "1", where saxitoxyn contains one hydrogen. [7]
This purine is highly hydrophilic [8] and thermostable, it is not destroyed by cooking. [9] Moreover, is very stable in usual storage, specially in acidic condition. [10]
NSTX blocks the extracellular portion, [11] the outer vestibule, [12] of some voltage gated sodium channels in a very powerful and reversible manner, without affection of other ion channels.
"Voltage-gated", also called "voltage-sensitive" and "voltage-dependent" sodium channel also known as "VGSCs" or "Nav channel" are crucial elements of normal physiology in a variety of animals, including flies, leeches, squid and jellyfish, as well as mammalian and non-mammalian vertebrates. This large integral membrane protein plays an essential role in the initiation and propagation of action potentials in neurons, myocytes and other excitable cells. [13]
Nav channels form the basis for electrical excitability in animals. Nav channels evolved from Ca2+ channels and were present in the common ancestor of choanoflagellates and animals, although this channel was likely permeable to both Na+ and Ca2+. Thus, like many other neuronal channels and receptors, Nav channels predated neurons. Invertebrates possess two Nav channels (Nav1 and Nav2), whereas vertebrate Nav channels are of the Nav1 family. [14]
Sodium-channel proteins in the mammalian brain are composed of an association that include one alpha subunit and one or more auxiliary beta subunits. Nine types of alpha subunits have been described (Nav1.1 to Nav1.9), and a tenth related isoform (Nax) may also play some role as a Nav channel. Based in this information, ten Nav classes can be described: Nav1.1 to Nav1.9, and Nax. [15]
Former five, [16] but more recently, six [17] neurotoxin receptor sites have been recognized between the seven receptor site [18] located in the vertebrate sodium channel receptor alpha subunit:
NSTX and other site 1 blockers have high affinity (very low dissociation constant) and high specificity for Nav channels. The action of NSTX produces minimal effect on cardiac Nav, where it exhibits about 20–60 fold lesser affinity than in Nav channels from rat skeletal muscle and rat brain. [19] Most data emphasize the role of "STX resistant" Nav channel 1.5 in human heart. [20] [21]
Toxins such as neosaxitoxin and tetrodotoxin have less affinity for most cardiac Nav channels than for most Nav channels in nerve tissue. Moreover, NSTX is so active on nerve Nav channel than is roughly a million-fold more potent than lidocaine. [22]
This mechanism of action can produce two well known kinds of effects in humans:
It can be approximately described using one of the classical model of neurotoxic disease, known from ancient times as red tide, the most harmful algal bloom (HAB). This well known clinical model is the "paralytic shellfish poisoning". [23]
Of course, there are great differences between different algal blooms, [24] [25] [26] [27] because of the mix of species included in each HAB, usually related to environmental conditions; [28] because of the levels and quality of PSTs produced in each HAB, that may be modulated by concurrent microorganism; [29] [30] [31] [32] and, last but not least, because of the specific properties of each kind of PST, for example:
In spite of its heterogeneous and poorly understood epidemiology, the clinical picture of PSP could be useful to anticipate clinical effects of systemic NSTX.
Usually, the victims of mild and severe acute intoxications eliminate the toxin in urine during the first 24 hours after ingestion, and improve to full recovery in the first day of intrahospital care (when vital support is provided in a timely manner). [40]
When outbreaks of PSP occur in remote locations, where medical assistance is limited, reported lethality is under 10% in adults, but can reach 50% in children younger than six years old. This difference could be secondary to dissimilar doses and composition of involved mixes of PSTs; delay in medical support; or some kind of susceptibility of children. [41] More recent information suggest that lethality could be around 1% of symptomatic patients, [42] including cases where air transportation was required from remote locations of Alaska. [43]
Electrophysiologic observations demonstrated sub clinical abnormalities lasting for some days [44] or weeks [45] after clinical recovery .
Some evidence suggest the presence of metabolic pathways for the sequential oxidation and glucuronidation of PST in vitro, both being the initial detoxication reactions for the excretion of these toxins in humans. [46]
Forensic analysis of fatalities after severe cases, conclude that PSP toxins are metabolically transformed by humans and that they are removed from the body by excretion in the urine and feces like any other xenobiotic compound. [47]
Considering the heterogeneous nature of toxins mixes contained in contaminated bivalve molluscs, the safe limit of toxin content in shellfish adequate for human ingestion is expressed in "saxitoxin equivalents". According to the Food and Agriculture Organization of the United Nations (FAO) and European Parliament, this limit is 80 microgram of saxitoxin equivalent per 100 gram of mussel meat (each mussel weights around 23 g). [48] [49] The U.S. Food and Drug Administration extends the same definition to "fish" quality, but the term "fish" refers to fresh or saltwater fin fish, crustaceans, other forms of aquatic animal life other than birds or mammals, and all mollusks; and incorporate the use of "ppm" as another measure for saxitoxin equivalent concentration in mentioned foods. [50]
Paradoxically, the chronic and/or repeated exposure to marine seafood toxins, which is a much more realistic phenomenon, has not been fully examined. [51] [52] One study in rats exposed to chronic (12 weeks) NSTX administration demonstrated some reduction in water and food intake, and a mild degree of transient cholestasis, probably associated to fasting, without other abnormalities. [53]
This action has been demonstrated in animals [54] and humans. [55] [56] [57] [58] [59]
The medical use of the NSTX anesthetic effect is supported by three reasons:
In conclusion, NSTX is a well defined molecule with a long-lasting and sometimes dangerous relationship with human subjects. Recent investigations suggest a clinical application as a new local anesthetic that sounds "too good to be true", but more investigation is required. [86]
A local anesthetic (LA) is a medication that causes absence of all sensation in a specific body part without loss of consciousness, providing local anesthesia, as opposed to a general anesthetic, which eliminates all sensation in the entire body and causes unconsciousness. Local anesthetics are most commonly used to eliminate pain during or after surgery. When it is used on specific nerve pathways, paralysis also can be induced.
Tetrodotoxin (TTX) is a potent neurotoxin. Its name derives from Tetraodontiformes, an order that includes pufferfish, porcupinefish, ocean sunfish, and triggerfish; several of these species carry the toxin. Although tetrodotoxin was discovered in these fish, it is found in several other animals. It is also produced by certain infectious or symbiotic bacteria like Pseudoalteromonas, Pseudomonas, and Vibrio as well as other species found in symbiotic relationships with animals and plants.
Batrachotoxin (BTX) is an extremely potent cardiotoxic and neurotoxic steroidal alkaloid found in certain species of beetles, birds, and frogs. The name is from the Greek word βάτραχος, bátrachos, 'frog'. Structurally-related chemical compounds are often referred to collectively as batrachotoxins. In certain frogs, this alkaloid is present mostly on the skin. Such frogs are among those used for poisoning darts. Batrachotoxin binds to and irreversibly opens the sodium channels of nerve cells and prevents them from closing, resulting in paralysis and death. No antidote is known.
Saxitoxin (STX) is a potent neurotoxin and the best-known paralytic shellfish toxin. Ingestion of saxitoxin by humans, usually by consumption of shellfish contaminated by toxic algal blooms, is responsible for the illness known as paralytic shellfish poisoning (PSP).
Bupivacaine, marketed under the brand name Marcaine among others, is a medication used to decrease sensation in a specific small area. In nerve blocks, it is injected around a nerve that supplies the area, or into the spinal canal's epidural space. It is available mixed with a small amount of epinephrine to increase the duration of its action. It typically begins working within 15 minutes and lasts for 2 to 8 hours.
Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks. These shellfish are filter feeders and accumulate neurotoxins, chiefly saxitoxin, produced by microscopic algae, such as dinoflagellates, diatoms, and cyanobacteria. Dinoflagellates of the genus Alexandrium are the most numerous and widespread saxitoxin producers and are responsible for PSP blooms in subarctic, temperate, and tropical locations. The majority of toxic blooms have been caused by the morphospecies Alexandrium catenella, Alexandrium tamarense, Gonyaulax catenella and Alexandrium fundyense, which together comprise the A. tamarense species complex. In Asia, PSP is mostly associated with the occurrence of the species Pyrodinium bahamense.
Sodium voltage-gated channel alpha subunit 9 is a sodium ion channel that in humans is encoded by the SCN9A gene. It is usually expressed at high levels in two types of neurons: the nociceptive (pain) neurons at the dorsal root ganglion (DRG) and trigeminal ganglion; and sympathetic ganglion neurons, which are part of the autonomic (involuntary) nervous system.
Anabaena circinalis is a species of Gram-negative, photosynthetic cyanobacteria common to freshwater environments throughout the world. Much of the scientific interest in A. circinalis owes to its production of several potentially harmful cyanotoxins, ranging in potency from irritating to lethal. Under favorable conditions for growth, A. circinalis forms large algae-like blooms, potentially harming the flora and fauna of an area.
Sodium channel blockers are drugs which impair the conduction of sodium ions (Na+) through sodium channels.
A channel blocker is the biological mechanism in which a particular molecule is used to prevent the opening of ion channels in order to produce a physiological response in a cell. Channel blocking is conducted by different types of molecules, such as cations, anions, amino acids, and other chemicals. These blockers act as ion channel antagonists, preventing the response that is normally provided by the opening of the channel.
Pao turgidus is a species of freshwater pufferfish native to the Mekong basin. It may also occur in the Chao Phraya basin in Thailand. This species grows to a length of 18.5 centimetres (7.3 in) SL.
Dinotoxins are a group of toxins which are produced by flagellate, aquatic, unicellular protists called dinoflagellates. Dinotoxin was coined by Hardy and Wallace in 2012 as a general term for the variety of toxins produced by dinoflagellates. Dinoflagellates are an enormous group of marine life, with much diversity. With great diversity comes many different toxins, however, there are a few toxins that multiple species have in common.
CgNa is a peptide toxin isolated from the sea anemone Condylactis gigantea. It causes an increased action potential duration by slowing down the inactivation of tetrodotoxin-sensitive sodium channels.
Toxin Cll1 is a toxin from the venom of the Mexican scorpion Centruroides limpidus limpidus, which changes the activation threshold of sodium channels by binding to neurotoxin binding site 4, resulting in increased excitability.
Antillatoxin (ATX) is a potent lipopeptide neurotoxin produced by the marine cyanobacterium Lyngbya majuscula. ATX activates voltage-gated sodium channels, which can cause cell depolarisation, NMDA-receptor overactivity, excess calcium influx and neuronal necrosis.
Gonyautoxins (GTX) are a few similar toxic molecules that are naturally produced by algae. They are part of the group of saxitoxins, a large group of neurotoxins along with a molecule that is also referred to as saxitoxin (STX), neosaxitoxin (NSTX) and decarbamoylsaxitoxin (dcSTX). Currently eight molecules are assigned to the group of gonyautoxins, known as gonyautoxin 1 (GTX-1) to gonyautoxin 8 (GTX-8). Ingestion of gonyautoxins through consumption of mollusks contaminated by toxic algae can cause a human illness called paralytic shellfish poisoning (PSP).
LmαTX3 is an α-scorpion toxin from Lychas mucronatus. that inhibits fast inactivation of voltage gated sodium-channels (VGSCs).
Decarbamoylsaxitoxin, abbreviated as dcSTX, is a neurotoxin which is naturally produced in dinoflagellate. DcSTX is one of the many analogues of saxitoxin (STX).
Beta-toxin Cll2, shortened to Cll2, is a toxin in the venom of the Mexican Scorpion species Centruroides limpidus limpidus. The toxin belongs to the β-class family of sodium channel-inhibiting scorpion toxins. It affects voltage-dependent activation, conductance and resurgent currents of voltage gated sodium channels by binding to site 4.
GiTx1 (β/κ-theraphotoxin-Gi1a) is a peptide toxin present in the venom of Grammostola iheringi. It reduces both inward and outward currents by blocking voltage-gated sodium and potassium channels, respectively.
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