Hunting for toxins across the Mediterranean Sea: an analytical strategy for facing the impending palytoxin threat

Blooms of Ostreopsis spp. once confined to tropical and subtropical areas have recently spread to more temperate regions such as the Mediterranean and the Southern-Atlantic coasts of Europe. In the last decade, O. confronta (cf.) ovata has become increasingly frequent with massive blooms with consequent relevant negative impacts on benthic communities and on human health through skin contact and toxic aerosols. Following the Mediterranean Ostreopsis-related outbreaks we developed a liquid chromatography-mass spectrometry method to be employed in the investigation of both field and cultured algal samples of O. cf. ovata. Our studies characterized O. cf. ovata as the producer of minute amounts of a putative palytoxin, one of the most potent marine toxins so far known, and of much higher amounts of several palytoxin congeners, that we named ovatoxins. Ovatoxin-a, the major component of most of the O. cf. ovata toxin profiles, has been recently isolated and structurally elucidated, while ovatoxin-b, -c, -d, -e, and -f have not been isolated yet. Toxin profiles of O. cf. ovata of different geographical origin can be quite different both qualitatively and quantivatively. In this joint presentation, the latest results of our research are outlined as follows: • LC-MS determination of the diverse toxin profiles of O. cf. ovata strains from all over the Mediterranean; • LC-MS detection of ovatoxins in seafood. This represents one of the main concerns to human health in the Mediterranean area. • LC-MS detection of ovatoxins in marine aerosols. This constitutes the first experimental evidence that respiratory distress in humans are linked to ovatoxins produced by O. cf. ovata during their blooms. • Preliminary toxicological data on ovatoxin-a. • Identification and characterization of the natural palytoxin-calcium complex by NMR and molecular modeling. This may pave the way towards the understanding of the mechanism of action of palytoxin at a molecular level.