Subchronic effects of cyanobacterial cells on the transcription of antioxidant enzyme genes in tilapia (Oreochromis niloticus)

The increasing occurrence of toxic cyanobacterial blooms in eutrophic water bodies is nowadays of worldwide concern due to their ability to produce toxins such as microcystins (MCs). These cyanobacterial toxins have been shown to affect aquatic organisms such as fish, resulting in oxidative stress. Among the antioxidant enzymes, glutathione peroxidase (GPx) and soluble glutathione-S-transferases (sGST) play an important role in the detoxification of MCs. In the present work tilapia (Oreochromis niloticus) were orally exposed to cyanobacterial cells containing MCs and non-containing MCs for 21 days. The activity and relative mRNA expression by real-time PCR of both enzymes and the GST protein abundance by Western blot analysis were evaluated in liver and kidney. Also the induction of lipid peroxidation (LPO) was assayed. MCs containing cyanobacterial cells induced an increase of LPO products in both organs, and MCs containing and MCs non-containing cyanobacterial cells altered the activity, gene expression and protein abundance of the enzymes, indicating the importance of GPx and sGST in MCs detoxification. Moreover, liver, the main organ involved in biodegradation and biotransformation, experienced an adaptative response to the toxic insult. These results show for the first time that the subchronic exposure to cyanobacterial cells causes changes in antioxidant and detoxification enzymes and that GPx and GST gene expression are good markers of these alterations in tilapia.