Microcystins toxic effects

The effects of cyanobacterial hepatotoxins and neurotoxins were examined on the embryos of fish and amphibians up to advanced stages of embryonic development. No acute toxic effects were observed after exposure to microcystins, but at the highest applied concentration of microcystin-LR (10 mg/L), morphological effects were detected. AN (400 pg/L) altered the heart rate in zebrafish, but no chronic effects were observed (Oberemm et al. 1999). The effects of cyanobacterial toxins on... 

Liu, Y, Song, L., Li, X. and Liu, T. The toxic effects of microcystin-LR on embryo-larval and juvenile development of loach, Miguruns mizolepis Gunthe, Toxicon, 40, 395, 2002. 

Protein phosphatases are ubiquitous. They are foxmd in all tissues and across species as diverse as mammals, plants, and bacteria, and they play a critical role in the regulation of multiple cellular metabolic pathways. Protein phosphatases reverse tiie active state of kinases through the hydrolytic removal of tiie phosphoryl group from kinases. The protein phosphatases inhibited by microcystins have broad substrate specificity and play roles in the regulation of a wide range of cellular fxmc-tions. Protein phosphatase 2A is highly conserved and is a major downregulator of active protein kinases in eukaryotic cells. Toxic effects in hepatocytes and other... 

Zhao, Y, Xie, P., Tang, R., et al., 2008. In vivo studies on the toxic effects of microcystins on mitochondrial electron transport chain and ion regulation in liver and heart of rabbit. Comp. Biochem. Physiol. Part C 148, 204-210. 

The ability to identify and quantify cyanobacterial toxins in animal and human clinical material following (suspected) intoxications or illnesses associated with contact with toxic cyanobacteria is an increasing requirement. The recoveries of anatoxin-a from animal stomach material and of microcystins from sheep rumen contents are relatively straightforward. However, the recovery of microcystin from liver and tissue samples cannot be expected to be complete without the application of proteolytic digestion and extraction procedures. This is likely because microcystins bind covalently to a cysteine residue in protein phosphatase. Unless an effective procedure is applied for the extraction of covalently bound microcystins (and nodiilarins), then a negative result in analysis cannot be taken to indicate the absence of toxins in clinical specimens. Furthermore, any positive result may be an underestimate of the true amount of microcystin in the material and would only represent free toxin, not bound to the protein phosphatases. Optimized procedures for the extraction of bound microcystins and nodiilarins from organ and tissue samples are needed. 

One role of cyanobacterial allelochemicals may be to alter the motility and distribution of competing photoautotrophs. In a recent study, Kearns and Hunter (2001) examined the effects of toxic metabolites from the filamentous cyanobacterium A. flos-aquae on a unicellular phytoplankton species, Chlamydomonas rein-hardtii. A. flos-aquae synthesizes both microcystins as well as anatoxins, providing the authors with an ecologically relevant opportunity to assess the individual and combinatorial effects of these toxins on an alga. 

Yuan, M., Namikoshi, M., Otsuki, A., and Sivonen, K. 1998. Effect of amino acid side-chain on fragmentation of cyclic peptide ions differences of electrospray ionization collision-induced decomposition mass spectra of toxic heptapeptide microcystins containing ADM Adda instead of Adda. EurMass Spectrom 4 287-298. 

Hermansky, S.J., Wolff, S.N., Stohs, S.J. (1990b). Use of Rifampin as an effective chemoprotectant and antidote against microcystin-LR toxicity. Pharmacology 41 231-6. 

Since a large number of microcystins has been already isolated and chemically characterized, mutations and modifications in the structure have allowed the identification of essential pharmacophores. The variable L-amino acid residues X and Y are most commonly Leu and Arg, respectively. But microcystin variants with both positions occupied by the basic Arg residue or by hydrophobic residues like Leu and Ala or Leu and Tyr are also produced by various Microcystis strains. While substitution of the Arg residue in position Y with hydrophobic residues or with Met(O) is without significant effect on the toxicity, replacement of the Leu residue in position X with Arg or Met(O) leads to significantly reduced toxicity (53). Variants with... 

Vezie, C. et al.. Effect of nitrogen and phosphorus on growth of toxic and nontoxic Microcystis strains and on intracellular microcystin concentrations, Microb. Ecol, 43, 443, 2002. 

Most of the available toxicological data on microcystins have been based on microcystin-LR. Other microcystin variants appear to be similar to microcystin-LR in their toxicological effects, but they differ in potency. Other factors that need to be taken into account when interpreting available data are that much of the data have been derived from experiments in rodents and rabbits using intraperitoneal injection as the route of exposure, and the extracts used in studies may consist of complex, crude mixtures of components derived from toxic algal blooms, or more or less purified and characterized components (Zhao et al., 2008, 2009). Extrapolation between routes of exposure and between the toxicities of different complex mixtures can make the comparison of data from different studies challenging. 

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