Abstract
Microcystins (MCs) are produced during the growth and proliferation of some species of cyanobacteria, mainly Microcystis aeruginosa, which has massive growth in eutrophic water bodies. Microcystins are highly toxic metabolites derived from some cyanobacteria species that exert its main effect in the liver through the inhibition of protein phosphatase (PP1 and PP2A). However, other damages in fish species are less documented and could be unexpected. The aim of the current study was to evaluate the effects of Microcystis aeruginosa extract (MaE) into the central nervous system (CNS) of the Nile tilapia. The MaE was normalized by MCs content (MC-LR). We include a positive control for protein phosphatase inhibition, norcantharidin intraperitoneally dosed at sublethal levels. On the eighth day, measurement of neurotransmission biomarkers (AChE, BChE, CbE, and GABA) were measured, as well as levels of mitochondrial calcium and the mitochondrial membrane potential by flow cytometry in the brain and spinal cord were assessed, in addition to the PP1/PP2A activity in the liver. The MCs elicited mortality at 5 µg/L. The positive control and MCs at sublethal levels inhibited the PP1/PP2A activity in the liver and induced alterations in the neurotoxicity biomarkers evaluated in the CNS. This response is probably due to the disruption of transport ions, dependent and independent of ATP because of alterations in the mitochondrial membrane potential and mitochondrial calcium. The findings of this study suggest that pollutants capable of inducing cyanobacterial blooms are able, in an indirect way, to exert neurotoxic effects in fish species through MC levels.
Highlights
Microcystins (MCs) are toxins produced by cyanobacteria, primarily Microcystis aeruginosa, forming blooms worldwide, in tropical and temperate environments
Juvenile specimens of Nile tilapia (Oreochromis niloticus) were obtained from a fish farm and were maintained under laboratory conditions in agreement with Article 38 and Chapter V of the Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010 for the protection of animals used for scientific purposes
The inhibition of the enzymatic activity of phosphatase 1 (PP1)/PP2A in the liver of the Nile tilapia elicited by the M. aeruginosa extract (MaE) was significantly decreased, even at doses of MC-LR considered safe (Fig. 1A)
Summary
Microcystins (MCs) are toxins (secondary metabolites) produced by cyanobacteria (blue-green algae), primarily Microcystis aeruginosa, forming blooms worldwide, in tropical and temperate environments. MCs are hepatotoxic cyclic heptapeptides released into the water during or on senescence of cyanobacterial blooms (Harada and Tsuji 1998; Malbrouck and Kestemont 2006). MCs are the most common of the cyanobacterial toxins found in freshwater, and are being often responsible for poisoning terrestrial animals, including livestock, wildlife, and humans who are exposed to MC-polluted water (Carmichael et al 2001). By these reasons, there is an increasing concern all over the world due to the acute and chronic effects on humans and wildlife from the MCs linked with water pollution. A large number of studies have documented the hazardous potential of MCs in aquatic organisms as well (e.g. Chorus and Bartram 1999; Landsberg 2002; Wiegand and Pflugmacher 2005; Olivares-Rubio et al 2015)
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