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Palytoxin is one of the most complex and biggest molecules known to show extreme acute toxicity. The dinoflagellate Ostreopsis spp., the producer organism of palytoxin, has been shown to be distributed worldwide, thus making palytoxin an emerging toxin. Rat-derived hepatocytes (Clone 9) and BE (2)-M17 human neuroblastoma cells were used to test palytoxin or palytoxin-like compounds by measuring the cell metabolic rate with Alamar Blue. The dose-dependent decrease in viability was specifically inhibited by ouabain in the case of BE (2)-M17 neuroblastoma cells. This is a functional, dynamic and simple test for palytoxins with high sensitivity (as low as 0.2 ng/ml). This method was useful for toxin detection in Ostreopsis extracts and naturally contaminated mussel samples. A comparative study testing toxic mussel extracts by LC (liquid chromatography)-MS/MS (tandem MS), MBA (mouse bioassay), haemolysis neutralization assay and a cytotoxicity test indicated that our method is suitable for the routine determination and monitoring of palytoxins and palytoxin-like compounds.

Background and Purpose: Dinoflagellates from the genus Ostreopsis have been related to the production of palytoxin and analogues. Based on that, this paper describes functional studies of crude extracts from Ostreopsis cf. siamensis collected in the Mediterranean Sea in order to biochemically characterize their toxic compounds., Methods: We compared the effects of 5 crude dinoflagellates extracts with a commercially available palytoxin and a purified Ostreopsis ovata extract on metabolic activity, membrane potential, and cytosolic calcium levels by using fluorescent dyes., Results: All the extracts resulted to be neurotoxic. In addition, all of them induced a membrane depolarization and a calcium increment that were abolished when preincubating with ouabain, an inhibitor of the Na(+)/K(+) pump., Conclusion: The effects observed were quite close to those induced by palytoxin and the Ostreopsis ovata extract as well, suggesting that Ostreopsis cf. siamensis is actually producing palytoxin-like compounds that are highly toxic and functionally active., (Copyright 2009 S. Karger AG, Basel.)