Cyanobacterium producing cylindrospermopsin cause oxidative stress at environmentally relevant concentrations in sub-chronically exposed tilapia (Oreochromis niloticus)

Abstract

Cylindrospermopsin (CYN) is a potent cyanobacterial cytotoxin produced by certain freshwater cyanobacteria. Structurally, it is an alkaloid with a tricyclic guanidine moiety combined with hydroxymethyluracil. It has proved to be a potent inhibitor of protein synthesis, and to deplete hepatic glutathione. Recently, some studies have shown that CYN produces changes in some oxidative stress biomarkers in fish acutely exposed to pure CYN by oral and intraperitoneal (i.p.) routes. In the present study tilapia (Oreochromis niloticus) were exposed by immersion to lyophilized Aphanizomenon ovalisporum cells added to the aquaria using two concentration levels, 10 or 100 μg CYN L(-1), during two different exposure times: 7 and 14 d. Fish were sacrificed and liver and kidney were extracted. The oxidative status of fish was evaluated by analyzing in both organs the following biomarkers: lipid peroxidation (LPO), protein oxidation, DNA oxidation, reduced-oxidized glutathione ratio (GSH/GSSG), and changes in the activity of Glutathione-S-transferase (GST), Glutathione Peroxidase (GPx), Superoxide dismutase (SOD), Catalase (CAT), and γ-Glutamyl-cysteine synthetase (GCS). In general, major changes were observed in tilapia treated with 100 μg CYN L(-1) after 14 d of exposure. However, some endpoints were altered at the lowest concentration assayed only after 7d of exposure, such as DNA oxidation and γ-GCS in kidney, and CAT and GSH/GSSG decrease in the liver and kidney. The kidney was the most affected organ. These findings confirm that the oxidative stress play a role in the pathogenicity induced by CYN in this fish species, and the results obtained could be useful for future ecotoxicological risks assessment studies, for the protection of fish and aquatic ecosystems. To our knowledge this is the first study dealing with the oxidative stress changes induced by cyanobacterial cells containing CYN and its derivative deoxy-CYN on fish exposed sub-chronically under laboratory conditions.