Abstract

Many marine invertebrates produce potent toxins, turning themselves poisonous as a defense strategy against predators. In contrast, other organisms can become poisonous by accumulating toxins from their own prey. Dinoflagellates are aquatic photosynthetic microbial eukaryotes, and some species produce highly toxic metabolites. These dinoflagellate toxins bioaccumulate up the food chain in various consumer organisms. Many filter-feeding organisms such as bivalves accumulate such toxins with no apparent adverse effects on them1 but causing intoxication when ingested by their predators, including fish and marine mammals, and ultimately also when humans consume contaminated seafood. Four major groups of dinoflagellate toxins have been described, namely, saxitoxins, ladder-shaped polyether compounds, long-chain polyketides, and macrolides.2 The dinoflagellate species Gambierdiscus toxicus produces several potent polyether toxins, some of which were initially identified in connection with a common type of food poisoning called ciguatera, caused by consumption of certain contaminated tropical and subtropical fish. Ciguatera involves a combination of gastrointestinal, neurological, and cardiovascular disorders. The two most common toxin classes associated with ciguatera are ciguatoxin (CTx) and maitotoxin (MTx), and they are among the most lethal natural substances known to man. Most of the neurological symptoms of ciguatera are caused by CTx, which exert their effects due primarily to the activation of voltage-gated sodium channels, causing cell membrane depolarization. MTx displays diverse pharmacological activities, which seem to be derived from its ability to activate Ca2+-uptake processes in a variety of cell types. MTx is the largest and most toxic known nonbiopolymeric toxin, with a molecular weight of 3422 Da. MTx is a very interesting compound given its extremely potent biological activity, and it has been used as a powerful pharmacological tool for the elucidation ofCa2+-dependent cellular processes.