TOXICOLOGY OF CYANOTOXINS: ON THE MICROCYSTINS

Abstract

revista vol 13 nº 2.indd revista vol 13 nº 2.indd

Cyanobacterial blooms are of worldwide concern as these microorganisms may produce toxins, including neurotoxins and hepatotoxins that can be seriously harmful to mammals and aquatic organisms. The most common type of cyanotoxin, microcystin, can affect the liver of vertebrates since hepatocytes are able to uptake it through the bile acid transporters. Microcystins are potent inhibitors of phosphatases 1 and 2A, by covalently and irreversibly binding to these enzymes. The ultimate consequence, when a lethal and acute dose is achieved, is hepatic hemorrhage. At sublethal and chronic doses, the toxin damages other tissues and promotes tumor formation. However, little is known about the toxicology, biodistribution and effects of long-term exposure to microcystins. Concern about the effects of such toxins on human populations are in fact quite recent. For instance, public health authorities began to realize the risk of the presence of cyanobacteria in water supplies only after an incident in 1996 in Caruaru (Northeast Brazil) resulting in the deaths of 100 patients from hemodialysis using microcystin-contaminated water. This led to the elaboration of specific laws regarding water quality control, including monitoring for cyanotoxins, making Brazil the first country to establish such a measure. This illustrates the importance of toxicological studies to assess the risk of cyanotoxins toward human populations.