Chemistry, etiology and determination methods of ciguatera toxins

Ciguatera refers tc, a type of human intoxication resulting from ingestion of tropical fish contaminated with ciguatoxin or its related toxins. Globally over 20,000 people are estimated to suffer from the poisoning. Though rarely fatal, the poisoning poses a serious threat to public health and tropical fisheries because of its unpredictable occurrence and implication of numerous fish species. Research effort undertaken by three institutions in the Pacific countries, finally led to discovey of the dinoflagellate, Gambierdiscus toxicus that produces ciguatoxin precursors, and determination of complex polyether structure of ciguatoxin C60H86O19, the principal toxin in ciguatera. A number of ciguatoxin analogs and related polyether compounds have been also determined. Investigation of ciguateric herbivorous fish resulted in finding of maitotoxin, which was later confirmed to originate from G, toxicus. Maitotoxin, one of the most complex natural products having the molecular formula C164H256O68S2Na2 was isolated, and its chemical structure has been successfully determined. The lethality of maitotoxin to mice (0.05 mu g/kg, i.p.) is only exceeded by a few proteins. The mechanism underlying its high potency is now explainable by its action to cause influx of extracellular Ca2+ ion across cell membrane. Other toxins of dinoflagellate origins include okadaic acid, prorocentrolide, amphidinol, and palytoxin analogs.