biotoxin is a poison produced by the metabolic activity of certain living beings, such as bacteria, plants, and fungi that serve as a biological defense, which protects the toxin-producer from being eaten. Many biotoxins can be further classified into what kind of effects they have on the body. Some of these groups include the following:

  • necrotoxins, substances that cause tissue destruction via cell death and are carried in the bloodstream.
  • neurotoxins, substances that affect the nervous system.
  • haemotoxins, substances that are carried in the bloodstream and target red blood cells.
  • cyanotoxins, produced by cyanobacteria.
  • cytotoxins, substances toxic at the level of the cell (kills individual cells).
  • mycotoxins, produced by fungi.
  • apitoxin, honey bee venom, injected via the sting.

Marine biotoxins are a group of substances toxic to higher animals that are formed in phytoplankton or other marine microorganisms and pass from them into fish tissues or shellfish through the food chain. Biotoxin-carrying fish species generally live in tropical and subtropical waters, in the seas of China and Japan, and in Australia. With the improvement of food preservation and freezing techniques and with the development of commercial trade of fish products, the problem of marine biotoxins has overcome the original geographical limits and has spread to almost the whole world.

The biotoxins certainly identified in fishery products are still few, but it is certain that the progressive pollution of the seas can establish biochemical processes capable of leading to the appearance of highly toxic substances. All these biotoxins have a very high toxicity, second only to that of tetanus and botulinum neurotoxins and cobra venom. In addition to tetrodotoxin and saxitoxin, very dangerous are the ciguatoxins, a group of less known substances with neurotoxic action, present in over 400 species of tropical or subtropical fish. These are generally edible species that in certain periods of the year accumulate the toxin perhaps as a result of ingestion of toxic algae.

Ciguatoxin poisoning manifests itself with symptoms similar to those of neurotoxic shellfish syndrome. Similar properties have the toxins of the dinoflagellide Gymnodinium breve, whose sudden and massive proliferation can give the sea a reddish color, red tide, with intense death of fish and seabirds. Bivalve molluscs, on the other hand, are resistant to the toxins of Gymnodinium and can accumulate them without damage, with consequent danger of food poisoning for man. No less toxic are other biotoxins, such as clupeotoxin, a substance of unknown composition responsible for severe intoxication by consumption of fish of the order Clupeiformes.

A toxic syndrome of hallucinatory type is caused by ichthyoallieinotoxin, a poison that can be present in the tissues of several genera of tropical fish belonging to the families Acanthurids, Mugillids, Pomacentrids and others. Also some species of sea turtles can cause food poisoning due to the content in their meat of biotoxin of which however at present little is known: among the species at higher risk the green turtle, the dermochelide and especially the hawksbill turtle.

Typical example of biotoxin from contamination is the scombrotoxin, the agent responsible for a benign and common form of intoxication due to the consumption of canned tuna or other Scombridi improperly stored. It would be due to the action produced by certain marine organisms on fish tissue.

Biotoxins in nature

Gram-positive bacteria secrete biotoxins (exotoxins, but today it is more correct to speak of extracellular protein toxins) in the districts colonized by them thanks to a regulated secretion system. Among the Gram-negative bacteria, Bordetella Pertussis and Vibrio Cholerae keep inside most of the toxic compounds (intracellular protein toxins) and release them only upon lysis. All other Gram-negatives express endotoxin or LPS as a surface toxic constituent, always released upon lysis and able to trigger inflammatory responses by contacting the specific TLR (Toll-like receptor) of the monocyte-macrophage system.

On the tentacles of some coelenterates, jellyfish in particular, there are stinging cells, the cnidocytes, which are activated when touched, thanks to a mechanoreceptor called cnidociglio, and extroflect stinging filaments called cnidae (from the greek κνίδα knìda, nettle). The cnidae inoculate a biotoxin that kills the prey by anaphylactic shock. The liquid urticant has therefore neurotoxic or hemolytic action, the nature of which may vary depending on the species, but usually consists of a mixture of three proteins with synergistic effect: hypnoxin, thalassin and congestin. Hypnoxin has an anesthetic effect, thus paralyzing; thalassin has an allergenic behavior that causes an inflammatory response; congestin paralyzes the circulatory and respiratory systems. Although not all jellyfish are stinging, some, such as cubomedusae, are particularly dangerous to humans: in some cases they can also cause death by anaphylactic shock.

Toxic plants produce toxins by means of their secondary metabolites: they are molecules that are produced outside the metabolic pathways that ensure the survival of the plant (and therefore considered primary). These molecules are quite widespread in the plant kingdom and are divided into four groups, namely:

  • the phenols: such as tannins, lignins, flavonoids and catechol-melanins.
  • the nitrogenous: the alkaloids, betalains, heterosides and glucosinolates.
  • the terpenes, which are resin elements of conifers.
  • nitrates, generally high concentrations are accumulated in some plants due to excessive use of fertilizers.
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