Apoptotic effect of cyanobacterial blooms collected from Polish water reservoirs

Recently in many countries, including Poland, the problem of toxicity of cyanobacterial blooms has been of great importance. In many cases it is connected with the increase of microcystins (MCYSTs) concentration in fresh water. This problem is caused by excessive eutrophication of drinking and recreational water bodies. In humans, the most frequent symptoms of the MCYST effect are: cutaneous rash, fever, vomiting, diarrhoea, gastroenteritis and acute damage of the liver. The aim of this work was to estimate apoptotic effects of five different cyanobacterial hepatotoxic extracts containing MC-LR and other variants of MCYSTs (MC-RR, MC-YR, and MC-WR). These effects were analysed in rat hepatocytes--primary target of cyanobacterial hepatotoxins. Morphological changes in hepatocytes were examined by means of fluorescence and differential interference contrast microscopy with the DNA-specific dye, Hoechst 33342. The hepatocytes were treated with each cyanobacterial extracts containing MC-LR in the range between 100 nM-2000 nM for 30 min, 60 min and 120 min. The first characteristic apoptotic changes: shrinking and budding of cells were seen after 30 min, MC-LR = 100 nM. During the next 30 min the percentage of apoptotic cells increased by over 50%, MC-LR at concentrations ranging from 100 to 250 nM (the value dependent on a bloom sample). Highly condensed chromatin and apoptotic bodies were observed in 85-90% of hepatocytes after 120 min of treatment with MC-LR in concentration of 1000 nM. The apoptotic changes in rat hepatocytes confirm the high cytotoxic potential of cyanobacterial bloom samples collected during different months and years from reservoirs of drinking and recreational water in central Poland.