Changes in the antioxidant metabolism in the embryonic development of the common South American toad Bufo arenarum: Differential responses to pesticide in early embryos and autonomous-feeding larvae

FERRARI A; ANGUIANO L; LASCANO C; SOTOMAYOR V; ROSENBAUM E; VENTURINO A

Journal of Biochemical and Molecular Toxicology

Wiley Periodicals, Inc

Año: 2008 vol. 22 p. 259 - 267

1095-6670

Amphibians may be critically challenged by aquatic contaminants during their embryonic development. Many classes of compounds, including organophosphorus pesticides, are able to cause oxidative stress which affects the delicate cellular redox balance regulating tissue modeling. We determined the progression of antioxidant defenses during the embryonic development of the South American common toad, Bufo arenarum. Superoxide dismutase and catalase activities were high in the unfertilized eggs, and remained constant during the first stages of development. Superoxide dismutase showed a significant increase when the gills were completely active and opercular folds began to form. GSH-reductase activity was low in the oocytes, and increased significantly when gills and mouth were entirely developed and the embryos presented a higher exposure to prooxidant conditions suggesting an environmental control. GSH content was also initially low, and rose continuously pointing out an increasing participation of GSH-related enzymes in the control of oxidative stress. GSH peroxidases and GSH-S-transferases showed relatively high and constant activities, probably related to lipid peroxide control. B. arenarum embryos have plenty of yolk platelets containing lipids which provide the energy and are actively transferred to the newly synthesized membranes during the early embryonic development. Exposure to the pro-oxidant pesticide malathion during 48 h did not significantly affect the activity of antioxidant enzymes in early embryos, but decreased the activities of catalase, GSH reductase and the pool of GSH in larvae. Previous work indicated that lipid peroxide levels were kept low in malathion-exposed larvae, thus we conclude that oxidative stress is overcome by the antioxidant defenses. The increase in the antioxidant metabolism observed in the post-hatching phase of development of B. arenarum embryo, thus constitutes a defense against natural and human-generated pro-oxidants present in the aquatic environment.