Abstract
Saxitoxin (STX) and its 57 analogs are a broad group of natural neurotoxic alkaloids, commonly known as the paralytic shellfish toxins (PSTs). PSTs are the causative agents of paralytic shellfish poisoning (PSP) and are mostly associated with marine dinoflagellates (eukaryotes) and freshwater cyanobacteria (prokaryotes), which form extensive blooms around the world. PST producing dinoflagellates belong to the genera Alexandrium, Gymnodinium and Pyrodinium whilst production has been identified in several cyanobacterial genera including Anabaena, Cylindrospermopsis, Aphanizomenon Planktothrix and Lyngbya. STX and its analogs can be structurally classified into several classes such as non-sulfated, mono-sulfated, di-sulfated, decarbamoylated and the recently discovered hydrophobic analogs—each with varying levels of toxicity. Biotransformation of the PSTs into other PST analogs has been identified within marine invertebrates, humans and bacteria. An improved understanding of PST transformation into less toxic analogs and degradation, both chemically or enzymatically, will be important for the development of methods for the detoxification of contaminated water supplies and of shellfish destined for consumption. Some PSTs also have demonstrated pharmaceutical potential as a long-term anesthetic in the treatment of anal fissures and for chronic tension-type headache. The recent elucidation of the saxitoxin biosynthetic gene cluster in cyanobacteria and the identification of new PST analogs will present opportunities to further explore the pharmaceutical potential of these intriguing alkaloids.
Highlights
The paralytic shellfish toxins (PSTs) are a group of naturally occurring neurotoxic alkaloids.Saxitoxin (STX) is the most researched PST to date, and since its discovery in 1957 [1], 57 analogs have been described
PSTs are primarily produced by the eukaryotic dinoflagellates, belonging to the genera Alexandrium, Gymnodinium and Pyrodinium [8,9,10]
Occurring PSTs may be structurally modified by various biological factors. These biotransformations can result in new PSTs that cannot be biosynthesized by cyanobacteria or dinoflagellates alone (Figure 2)
Summary
The paralytic shellfish toxins (PSTs) are a group of naturally occurring neurotoxic alkaloids. A novel group of PSTs with a hydrophobic side chain were identified within the cyanobacterium Lyngbya wollei and are characterized by the presence of an acetate at C13 (LWTX 1–3,5,6) and a carbinol at C12 (LWTX 2,3,5) in place of a hydrated ketone [82] This was the first report of STX derivatives with a hydrophobic substituent and these toxins have only been found exclusively in the freshwater environment [14,82]. Negri et al reported a novel subclass of analogs containing a hydrophobic R4 side chain designated GC1-3 These were first isolated and structurally characterized from Australian isolates of the dinoflagellate Gymnodinium catenatum and since have been identified within. Improvement of detection methods will no doubt uncover new natural forms of STX, we are still only beginning to understand the mechanisms by which these complex molecules are produced in nature
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