Toxicity of microcystin from cyanobacteria growing in a source of drinking water

Microcystin-LR (MC-LR) is a cyanobacterial heptapeptide that presents acute and chronic hazards to animal and human health. The morphological changes in mitochondria are the primary effect induced by MC-LR leading to cell death. We investigated the toxicity of cyanobacterial microcystin-containing extract (CEM) on the respiratory complex of mammalian mitochondria from Bos taurus. Cyanobacterial blooms of Microcystis aeruginosa were harvested from Sulejow Reservoir, a source of drinking water in central Poland. The concentration of microcystin-LR (MC-LR(CEM)) in CEM extract was determined by high-performance liquid chromatography (HPLC). Commercially available microcystin-LR (Sigma) was used as a standard (MC-LR(S)); both standard and CEM extract were incubated with mitochondria in different doses and time of exposure. MC-RL(CEM) at 1 nM, maximal acceptable dose of microcystin (WHO) in drinking water, provoked activation of cytochrome c oxidase complex in mitochondria. We suggest that it might be considered as a defensive signal of mitochondria against low concentration of a toxic compound. In contrast 1 iM MC-RL(CME) inhibited the activity of mitochondrial oxidase complex much stronger than the same concentration of standard MC-RL(S) (58% vs. 87% of control activity, P<0.05), and this may cause a similar effect to long-term consumption of water. In conclusion, we affirm that CEM extract is highly toxic, and mitochondria could be used as an indicator of this toxicity in vivo, especially during long-term consumption of water from reservoirs where microcystin is produced.