Pelander A., Ojanperä I., Vuori E.

Department of Forensic Medicine, PO Box 40, F1N-00014, University of Helsinki, Finland

Cyanobacterial blooms are common in fresh and brackish waters, especially in the late summer season. At least half of the blooms produce neuro- or hepatotoxins, the hepatotoxic blooms being more common. The hepatotoxins, known as microcystins and nodularins, are powerful natural toxins with LD₅₀ values of 60-70 µg/kg (i.p. mouse) for the majority of the variants. Annual blooms cause potential health hazards in recreational waters and in drinking water reservoires.
Microcystins are cyclic heptapeptides consisted of five constant D- amino acids and two variable L-amino acids. More than 50 closely related structural variants are known. Nodularins are cyclic pentapeptides with three D- amino acids and two L-amino acids. The key structural element connected with toxicity is the novel D-ß-amino acid named Adda, common for both microcystins and nodularins. The general structure and the principles of structural variation will be presented.
At present three methods, namely mouse bioassay, high performance liquid chromatography and enzyme inhibition assay are mainly utilised when analysing cyanobacterial hepatotoxins. An efficient screening method has not been developed so far. Thin layer chomatography is a potential technique for the high capacity screening analysis of peptide hepatotoxins. The benefits and the drawbacks of these and other methods will be discussed.