Saxitoxin: what is it?
Paralyzing bivalve poison is the least known expression that indicates STX, or saxitoxin : it is a powerful water-soluble marine toxin, synthesized by microscopic algae - known as dinoflagellates - belonging to the Alexandrium genus, in particular Alexandrium tamarense, Alexandrium minutum (present in the Adriatic), and Gymnodinium catenatum . Also cyanobacteria, or blue algae, constitute a potential source of STX.
STX is among those responsible for the bivalve mollusc syndrome (or PSP, which stands for Paralityc Shellfish Poisoning ), which causes symptoms ranging from mild tingling and numbness of the lips to full-fledged respiratory paralysis with a poor prognosis.
The term Saxitossina, or STX, derives from the mollusc Saxidomus giganteus, in which the toxin was isolated for the first time: it is infected by eating contaminated phytoplankton (eg dinoflagellates).
Currently, STXs have been isolated in many filter-feeding bivalve molluscs, such as mussels, oysters, scallops and clams.
STX: molecule analysis
The STX molecule is a carbamate with the substituent in position 4; in chemistry, saxitoxin is known with the brute formula C 10 H 19 N 7 O 4 ; it is a heterocyclic polar alkaloid containing the structural skeleton of peridropurin. It is an insoluble substance in organic solvents and soluble in water, whose toxicity is given by guanidine groups, also responsible for the basicity of the compound.
It was not until 1977 that the STX was synthesized in the laboratory.
Currently, over 20 varieties of STX have been isolated, synthesized by microorganisms and molluscs; other bivalve species may contain but not synthesize saxitoxin.
In medicine, STX is considered one of the most potent and most dangerous naturally occurring toxic compounds: it is estimated that the lethal dose ip (intra-peritoneum) in the mouse is 1, 250 times lower than in sodium cyanide. Furthermore, it is observed that in mice the LD50 is around 3.5 μg / kg by intravenous route and 260 μg / kg per os.
STX is resistant to high temperatures (thermostability): it is estimated that by boiling the contaminated mollusc at a pH of 3, STX degrades after 3 hours [taken from the poisonous marine animals and their toxins, by F. Ghiretti and L. Cariello]
STX: mechanism of action
Saxitoxin works by inhibiting nerve transmission: the toxin blocks the sodium channels, without affecting potassium permeability.
We have seen that saxitoxin has guanidine groups which give the molecule its peculiar toxicity: these groups, positively charged, are permanently bonded with the COO- (ionized carboxylic group), creating a block of the sodium channel. Considering that the sodium channels are located near the heart, muscle cells and neurons, it is clear that blocking these causes very heavy consequences in the body.
Furthermore, STX appears to be responsible for the functional alteration of some enzymatic catalysts.
| STX: sodium channel block → obstruction of nerve impulse transmission along neurons → inhibition of acetylcholine release → impossibility of communication between neurons and muscle cells → death by respiratory arrest |
STX intoxication: symptoms
Once again, the well-known Paracelsus statement is absolutely valid: "it is the dose that makes poison ": the symptoms derived from STX intoxication depend on the dose taken. Generally, after a period of time varying from 30 minutes to 2 hours, the symptoms begin with tingling, and then continue with marked muscular asthenia, altered sensitivity to the lips, tongue, hands, feet, scalp and face, alterations of the movement and ataxia. Sometimes these symptoms are also associated with cardiovascular collapse and hypothermia [from //it.wikipedia.org/]
therapies
As for TTX (tetrodotoxin), there is no anti-poison against STX intoxication: in this regard, the therapy is symptomatic and involves a gastric lavage to be performed within the shortest interval of time possible from the intake of the toxic substance; the use of alkaline substances is also recommended to inactivate saxitoxin. In case of respiratory deficit, artificial respiration is recommended.
Prognosis
In case of severity, the prognosis is poor and death occurs after 3-12 hours for respiratory paralysis. Generally, when the STX intoxicated patient exceeds 12 hours after taking the substance, the prognosis is good.
It is estimated that the mortality rate for STX intoxication varies from 1 to 22%, a clearly very wide range since, as we have seen, the severity of intoxication is proportional to the amount of toxin taken.
Summary
STX: to fix the concepts
Synonym: Bivalve paralyzing poison
- Filter-feeding bivalve molluscs (mussels, oysters, scallops and clams)
- Microscopic algae (dinoflagellates)
- Blue algae
- Chemical formula : C 10 H 19 N 7 O 4
- General description : carbamate with the substituent in position 4. It is a heterocyclic polar alkaloid containing the structural skeleton of peridropurine
- Solubility : insoluble in organic solvents and soluble in water
- Toxicity : given by guanidine groups, also responsible for the basicity of the compound
- Currently isolated STX varieties: 20 varieties of STX, synthesized by microorganisms and molluscs
- Lethal dose ip (intra-peritoneum) in the mouse: 1, 250 times lower than sodium cyanide
- LD50 in the mouse: it is around 3, 5 μg / Kg via ev
- LD50 in the mouse: 260 μg / kg per os
Death occurs by respiratory arrest
- Onset: tingling, marked muscular asthenia, altered sensitivity to the lips, tongue, hands, feet, scalp and face, movement alterations and ataxia
- Cardiovascular collapse and hypothermia (less frequent)
- Death by respiratory arrest
- There is no anti-poison against STX intoxication
- Symptomatic therapy
- Artificial respiration
- Administration of alkaline substances to inactivate saxitoxin
- Gastric lavage
When the patient exceeds 12 hours after STX: good prognosis
