Paralytic shellfish toxins (PSTs) are non-protein neurotoxins produced by saltwater dinoflagellates and freshwater cyanobacteria. They are a group of water-soluble carbamate alkaloids, which are either non-sulfated (saxitoxin (STX), neo-STX), singly-sulfated (gonyautoxins (GTX)) or doubly-sulfated (C-toxins). A high intake of PST leads to paralytic shellfish poisoning, where the toxins block the influx of sodium channels, restricting signal transmission along neurons therefore causing death from respiratory failure. The effect of long-term, low level exposure to PSTs is unknown, however most cases where humans are affected occur through contaminated seafood (such as mussels and oysters), algal dietary supplements and toxin-producing cyanobacterial cells. Human paralytic poisoning has been an increasing problem in the food industry, where seafood regulations set the maximum acceptable limit of PSTs in shellfish at 80 µg STC equivalents 100g-1 tissue. There is no known antidote or cure for paralytic shellfish poisoning, and most methods involving removing PSTs have limitations.
This study by
Vasama et al. (2014) looks at using two probiotic lactic acid bacteria, Lactobacillus rhamnosus strains GG (GG)
and LC-705 (LC-705) (in viable and non-viable form), in removing six PSTs from
acidic and neutral solutions, mimicking the pH variation in the
gastrointestinal tract. Both bacterial strains (GG and LC-705) in both viable
and non-viable forms were cultured, and cyanobacterial extract containing PSTs
(taken from a bloom of toxic Anabaena
circinalis) were obtained and prepared to give two pH level solutions. Pure
PST solution was prepared and each strain of bacteria was suspended in either Pure
PST solution (as a control) or one of the two pH PST solutions (pH 7.3 or 2.0).
High Performance liquid chromatography was then performed on the samples to
detect each of the three classes of PSTs (STXs, GTXs and C-toxins).
The results
showed a strong removal of PSTs by non-viable bacteria indicating that PSTs are
possibly removed by binding rather than metabolism. The highest degree of
removal was observed for STX and neoSTX (77%-97.2%). The effect of non-viable and
viable showed no significant difference therefore suggesting viable bacteria
may also remove PSTs through binding, which is consistent with previous reports
that specific bacterial strains remove a range of mycotoxins through binding.
Overall, our knowledge
on absorption of PSTs through mammalian intestinal epithelium is still limited,
however this is the first study to show that by possibly altering the intestinal
microflora composition using probiotics, the uptake of harmful compounds by the
body when ingesting PSTs can be decreased and symptoms of sickness can be prevented.
This can therefore lead to development for industrial applications or health
benefits.
Vasama, M., Kumar, H., Salminen, S. & Haskard, C. A.,
2014. Removal of Paralytic Shellfish Toxins by Probiotic Lactic Acid Bacteria. Toxins,
Volume 6, pp. 2172-2136.
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