There are four forms of poisoning caused by consumption of contaminated seafood, which markedly differ in course and symptoms: paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP) and diarrhetic shellfish poisoning (DSP). In addition, ciguatera fish poisoning (CFP) is a disorder associated with dinoflagellate toxins that accumulate in tropical fish meat. ASP can be a life-threatening syndrome. It is characterized by gastrointestinal symptoms such as nausea, vomiting, abdominal cramps and diarrhea as well as neurological symptoms. DSP causes gastrointestinal symptoms only. This disease is not fatal and characterized by severe diarrhea, nausea, vomiting, abdominal cramps and shivers. In contrast, NSP causes an intoxication syndrome with both neurological and gastrointestinal symptoms. NSP toxins can also cause respiratory asthma-like symptoms by formation of toxic aerosols through wave movements. PSP is a life-threatening syndrome like ASP. The symptoms are purely neurological and the onset is fast. The main PSP toxins are saxitoxins and gonyautoxins, NSP toxins are brevetoxins, ASP toxins are domoic acid and DSP toxins are okadaic acid, dinophysistoxins, pectenotoxins, azaspiracids and yessotoxins. Toxins causing ASP, DSP and PSP may be present in European waters, while NSP toxins could be found in imported shellfish. The chemical structures underlying the ASP, DSP NSP and PSP toxins are known. The toxic dinoflagellates producing them can be isolated from both natural and anthropogenic algal blooms. The chemical structures of the ciguatera toxins are not well known except that of ciguatoxin; the structure of maitotoxin is only partly understood.
Several unicellular eukaryotic dinoflagellates responsible for toxic algal blooms in coastal waters have been isolated and their toxin profiles determined. Saxitoxin (and its 18 derivatives), responsible for PSP, has been found in various dinoflagellates. Another dinoflagellate toxin, tetrodotoxin, accumulates in crab and in puffer fish feeding on bivalves that have enriched the toxin. Saxitoxin and tetrodotoxin are specific blockers of voltage-dependent sodium channels, causing muscle paralysis through their effect on the action potential.
Brevetoxins, gonyautoxins and saxitoxin are neurotoxins, which affect voltage-dependent sodium channels; they are not cytotoxins. In contrast to them, yessotoxin that is structurally closely related to brevetoxin B does not potentiate such channels, but shows cytoxicity and different toxicological properties. The DSP toxin okadaic acid, which is produced by the marine dinoflagellate Prorocentrum lima, is a specific inhibitor of serine/threonine phosphatases 1 and 2A. Okadaic acid can induce apoptosis in human cell lines. P1 could show that okadaic acid causes an increase in activity of caspases in primary neuronal cells.
