In vitro and in vivo evaluation of paralytic shellfish poisoning toxin potency and the influence of the pH of extraction.

Paralytic shellfish poisoning (PSP) is one of the most severe forms of food poisoning. The toxins responsible for this poisoning are natural compounds, which cause the arrest of action potential propagation by binding to voltage-gated Na+ channels. Several standards for PSP toxins are nowadays commercially available; however, there is not accessible data on the biological activity of the toxins present on this standards and their in vivo toxicity. We have developed an in vitro quantification method for PSP toxins using cultured neurons and compared the potency of the commercial PSP toxin standards in this system with their relative toxicity by mouse bioassay. The in vitro potencies of the PSP toxin standards were saxitoxin (STX) > decarbamoylsaxitoxin (dcSTX) = neosaxitoxin (NeoSTX) > gonyautoxins 1, 4 (GTX1,4) > decarbamoylneosaxitoxin (dcNeoSTX) > gonyautoxins 2, 3 (GTX2,3) > decarbamoylgonyautoxins 2, 3 (dcGTX2,3) > gonyautoxin 5 (GTX5). The data in vitro correlated well with the toxicity values obtained by mouse bioassay. Using this in vitro model we also provide the first data evaluating the potencies of PSP toxins after extraction in acidic pHs, indicating that the toxicity of the sample increases in acidic conditions. This observation correlated well with the chemical transformations undergone by contaminated samples treated in several acidic conditions as corroborated by high-performance liquid chromatography (HPLC) detection of the toxins. Therefore, a variation of 2 units in the pH during PSP extraction may lead to large discrepancies regarding sample lethality during official PSP control in different countries. The results presented here constitute the first comprehensive and revised data on the potency of PSP toxins in vitro and their in vivo toxicity.