Hepatotoxicity associated with microcystin

Abstract

Urban and industrial discharges, intense agricultural exploitation and fisheries have been causing the eutrophication in both drinking and recreational waters. A frequent consequence of eutrophication in waters is the massive development of cyanobacteria. The occurrence of these blooms induces a severe problem, as Microcystis aeruginosa, the most widespread distributed cyanobacteria, can produce microcystins (MC). Toxic effects of MC have been described in liver, lungs, stomach, and intestine. Deaths in wildlife, livestock and human beings were also associated with MC exposition. MC exposition can occurs directly by ingestion, inhalation, contact, intravenous inoculation of contaminated water (hemodialysis) or indirectly, by the consumption of animals, as fish and mollusks, the majors ingestors of cyanobacteria and its toxins. The most toxic MC, an also the most common is microcystin-LR (MC-LR), that has the liver as the main target organ. Microcystin is taken up specifically into the liver by bile acid transporters and, after entering the cytoplasm, inhibit protein phosphatases 1 and 2A, which leads to the increase in protein phosphorylation. This effect has two main consequences: the destruction of cytoskeleton directly causing cytotoxic effects, and deregulation of cell division, leading to tumor-promoting activity. Acute exposition to MC induces severe intrahepatic hemorrhage, necrosis and apoptosis, while chronic exposure can cause hepatic or intestinal neoplasia. It has been documented that MC hepatotoxicity is closely associated with intracellular reactive oxygen species formation. Natural degradation of microcystins depends on the solar radiation and bacteria. If degradation is insufficient, MC will persist in the freshwater food chain. Microcystin contamination of waters is therefore a hazard to human and animal health, so efforts to avoid eutrophication of waters sources are essential, in order to minimize the risks to public health.