Anatoxin characterization

The main genera responsible for freshwater toxic blooms are Microcystis, Anabaena, Aphanizomenon and Oscillatoria. Toxins produced include 1. anatoxins, alkaloids and peptides of Anabaena 2. the peptide microcystin and related peptides of Microcystis 3. aphantoxins, compounds of Aphanizomenon with properties similar to some paralytic shellfish poisons. Properties of Oscillatoria toxin suggest they are peptides similar to those of Microcystis. Microcystis toxins are peptides (M.W. approx. 1200) which contain three invariant D-amino acids, alanine, erythro-3-methyl aspartic and glutamic acids, two variant L-amino acids, N-methyl dehydro alanine and a 3-amino acid. Individual toxic strains have one or more multiples of this peptide toxin. The one anatoxin characterized is a bicylic secondary amine called anatoxin-a (M.W. 165). The aphantoxin isolated in our laboratory contains two main toxic fractions. On TLC and HPLC the fractions have the same characteristics as saxitoxin and neosaxitoxin. 

Anatoxins. Neurotoxins produced by filamentous Anabaena flos-aquae are called anatoxins (ANTXS) 15). Currently two anatoxins, from different strains of A. flos-aquae, have been isolated and at least partially characterized. ANTX-A from strain (single filament isolate) NRC-44-1 is the first toxin from a freshwater... 

Cyanobacteria toxins are toxins produced by certain species of blue-green algae that have become a major environmental and public health concern. The behavior of cyanotoxins during chlorination treatment has been recently reviewed by Merel et al. [129]. Chlorination DBFs have been reported only for the hepatotoxins microcystin-LR and cylindrospermopsin. Other cyanotoxins, such as nodularins, saxitoxins, and anatoxins, have yet to be investigated. Different isomers of six chlorination products of microcystin-LR have been characterized dihydroxy-microcystin, monochloro-microcystin, monochloro-hydroxy-microcystin, monochloro-dihydroxy-microcystin, dichloro-dihydroxy-microcystin, and trichloro-hydroxy-microcystin. Only two chlorination DBFs have been reported so far for cylindrospermopsin 5-chloro-cylindros-permopsin and cylindrospermopsic acid [129]. Chlorination of microcystin, cylindrospermopsin, and nodularins seems to reduce the mixture toxicity however, this aspect has not been extensively studied [129]. 

The synthetic aspects of anatoxin-a (AN) and analogues are discussed in a separate chapter of this text, and the analytical methods for anatoxins are the subject of a separate review to be published elsewhere. A number of reviews have demonstrated the importance of understanding toxic cyanobacteria as potential environmental and health hazards as well as a resource of bioactive molecules (Harada 1999 Skulberg 2000 Briand et al. 2003). AN was one of the first cyanobacterial toxins to be chemically and functionally characterized and its high neurotoxicity has attracted extensive research activity. 

Anatoxins are alkaloids produced exclusively by the cyanobacterial genera Anabaena, Planktothrix, and Aphanizomenon. Anatoxin-a (Figure 1C), the first cyanobacterial toxin to be chemically and functionally characterized in 1972, is a secondary amine whose ionization state varies with the pH (pfCa = 9.4). This compound is highly polar and fully soluble in water. Its methylated derivative homoanatoxin-a presents very similar properties. At elevated pH (above 10), both toxins become unstable and degrade very quickly into nontoxic analogs. 

Anatoxin-a(s) has been detected in toxic blooms in lakes in Canada [4], Denmark [123, 124], and Brazil [125, 126]. So far, only a few cyanobacterial strains producing anatoxin-a(s) have been characterized Anahaena flos-aquae [4], Anabaena crassa [126], and Anabaena lemmermannii [124]. The detection methods used to assay anatoxin-a(s) rely on the colorimetric assay for acetylcholine esterase [5], or on an electrochemical biosensor based on acetylcholine esterase activity [127,128], or more recently on the use of LC-MS [129]. 

Aracava, Y, Deshpande, S.S., Swanson, K.L., et al., 1987. Nicotinic acetylcholine receptors in cultured neurons from the hippocampus and brain stem of the rat characterized by single channel recording. FEES Lett. 222 (1), 63-70. Aronstam, R.S., Witkop, B., 1981. Anatoxin-a interactions with cholinergic synaptic molecules. Proc. Nat. Acad. Sci. USA 78 (7 I), 4639-4643. 

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