Effects of Microcystins, Cyanobacterial Toxins, on Mammalian Cells and Organs

Microcystins are hepatotoxic cyclic heptapeptides characterized by the presence of non proteinogenic β-amino acid ADDA. They are produced by numerous bloom forming cyanobacterial genera. Acute lethal intoxications of humans are rare, but especially chronic exposure to these toxins presents a serious threat to the health of human population. Microcystins enter cells mostly via bile acid transporters; therefore liver is the main target organ in acute intoxication. It has been shown that microcystins are potent inhibitors of intracellular protein phosphatases 1 and 2A. This leads to hyper- phosphorylation of a number of intracellular structural and signal proteins, activation of caspases, and apoptosis of the affected cells. Tumour promoting effects of microcystins have also been described. Considering reports by several authors showing harmful effects of long term exposure to microcystins in several highly populated regions of the planet it must be emphasized that high safety measures should be taken in monitoring the quality of water and food used in human nutrition and medical care.