CHANGES OF SUPEROXIDE DISMUTASE IN TILAPIA FISH (OREOCHROMIS SP) EXPOSED TO EXTRACTS OF MICROCYSTIN-CONTAINING CYANOBACTERIA

摘要

Aerobic organisms are protected against oxidative stress by antioxidant systems, including the radical scavenging enzyme superoxide dismutase (SOD), which catalyses conversion of O_2~- to H_2O_2. In this work, we have characterized the active isoforms of SOD in tilapia fish (Oreochromis sp.), and analyzed their alteration after exposure to Micro-cystin (MC)-containing cyanobacteria extracts. Fish were exposed intraperitoneally to a dose of 725 μg/kg MC-LR, and sacrificed after 24 h and 7 days. Lipid peroxidation (LPO), as well as total SOD activity, was measured in the homogenates of liver, kidney, muscle, intestine, heart and gills. Active isoSODs were revealed after their separation by polyacrylamide gel electrophoresis under non-denatured conditions. The identification of the diverse SOD isoforms was attained by the use of specific inhibitors (cyanide and hydrogen peroxide). In all fish organs two isoforms were detected: a major one, of the Cu/Zn type, and a minor one, of the Mn-SOD type. MC-extract exposure produced a reduction of total SOD activity in the liver, kidney, heart, muscle and gills. This SOD activity decrease could be due to the oxidative stress induced by exposure to MCs, as indicated by the enhancement of LPO detected. In all fish organs the isoSODs were differentially inhibited, the most affected isoform appearing to correspond to a Cu/Zn-SOD.