Profile of markers of stress and biotransformation of sea lamprey juveniles from Minho river basin during salinity acclimation

Abstract

Recent studies seem to point out to the decline of Portuguese populations of sea lamprey Petromyzon marinus (Petromyzontidae) (Cabral, 2005). Especially, during its trophic migration, the gill epithelium of sea lamprey juveniles undergoes marked changes which could be disturbed by chronic oxidative stress events triggered by chemical factors, like unusual presence of a pollutant in the lamprey habitat which could cause damages in the chloridric cells. Some antioxidant enzymes, such as CAT T and GPx that detoxify H2O2 in water; GST, conjugation enzymes that detoxify organic pollutants or GSH which contributes to preserve the reducing environment of the cell can be frequently used as markers of cell health. Therefore, the main goal of this study was to evaluate the profile of stress and biotransformation markers of macrophthalmia from Minho river basin during salinity acclimation. Sampling occurred at the beginning of the sea lamprey downstream migration in the Minho river basin. The sampled sea lamprey juveniles (i.e. macrophthalmia) were transported live to the laboratory in appropriate life support conditions and separated in three groups: i) macrophthalmia maintained at 0 PSU for 7 days; ii) macrophthalmia maintained at 0 PSU for 30 days and iii) macrophthalmia subjected to NaCl gradient up to 35 PSU, during 30 days in aquarium. Cytosol and microsomes obtained by differential centrifugation of gills homogenates, prepared in 50 mM Tris-HCl pH 7.5 buffer, were stored at -80 °C for subsequent determination of ROS (LeBel, 1990), MDA (Ohkawa, 1979), GSH and GSSG (Hissin, 1976) contents as well as CAT T (Beers, 1952), GPx (Flohé, 1984), mGST (Habig, 1974) and cGST (Habig, 1974) activities by fluorescence and spectrophotometry UV/Vis, respectively. The results show that salinity acclimation caused a significant increase in thiols content and a significant decrease in the GSH/GSSG ratio, ROS content and cGST activity (p <0.05). The increase in glutathione content of gills seems to compensate a reducing-oxidant transition induced by salinity. However, the decrease in GSH/GSSG ratio and cGST activity allowed inferring an insufficient regeneration of GSH by glutathione cycle. This response also suggests that gills of sea lamprey macrophthalmia from Minho river basin, probably decreases its detoxication ability of organic pollutants during trophic migration. This response may eventually compromise the seawater acclimation success of juvenile sea lampreys that are exposed to certain pollutants.