Differential detoxification and antioxidant response in diverse organs of Corydoras paleatus experimentally exposed to microcystin-RR.

We assessed changes in activities of both detoxification and antioxidant enzymes as well as lipid peroxidation levels in liver, gill, intestine and brain of Corydoras paleatus exposed to dissolved microcystin-RR (MC-RR). Fish were captured at an unpolluted area, transported to the laboratory, and acclimated previous to experiments. Exposures were carried out using MC-RR at 0.5, 2, 5 and 10 microg L(-1). After exposures for 24h, fish were sacrificed and dissected separating liver, gills, intestine and brain of each fish. Organs were used for enzyme extractions, evaluating both antioxidant and detoxification systems through the assay of glutathione reductase (GR), guaiacol peroxidase (POD), glutathione peroxidase (GPx), catalase (CAT) as well as glutathione S-transferase (GST). Additionally, thiobarbaturic acid (TBA) method was used to evaluate the peroxidation of lipids (LPO). GST was inhibited in all studied organs at most MC-RR concentrations used. Activities of GR, POD and GPx were enhanced in liver at 2 microg L(-1), but inhibited in gills at all tested concentrations. CAT activity was enhanced in liver at all studied concentrations. Antioxidant response in liver is activated at low toxin concentrations, followed by a drop at the highest MC-RR levels. On the contrary, detoxification activity is inhibited in liver and brain in a dose-dependent way. On the other hand, MC-RR (>or=2 microg L(-1)) induced LPO in brain of exposed fish, but not in other organs. This finding becomes to this organ in one of the most severely affected. Results show that gills are also very affected, since both antioxidant and detoxification systems were inhibited in this tissue. Thus, inhibition of these defense systems could increase the uptake of different toxics through gills of fish exposed to dissolved MC-RR, leading to an increased health risk for fish. The different response observed on diverse organs exposed to MC-RR might be related to the uptake route as well as on biotransformation and bioaccumulation capabilities of different studied organs.