Polyamine metabolism in the exposure to organophosphorus pesticides of amphibian embryos from North Patagonia, Argentina

LASCANO, CECILIA; PIRES, NATALIA SUSANA; CESCHIN, DANILO GUILLERMO; VENTURINO, ANDRÉS

Tivoli

Conferencia; 4th International Conference on Polyamines: Biochemical, Physiological and Clinical Perspectives; 2016

The northern patagonic region is the main productive area of pears and apples in Argentina, where organophosphorus(OP) pesticides have been historically applied in large quantities for pest control. In order to contribute to responsible decision-making, our group has analyzed the impact of pesticide application on aquatic organisms for more than35 years. For decades, the insecticide azinphos-methyl (AM) was the main OPpesticide employed; it has been detected in surface and groundwater in North Patagonia, exceeding the criteria for protection of aquatic life and remaining at high concentrations throughout the season (Tosi et al., 2009). Rhinella arenarum is a native toad to Argentina which spends its embryonic and larval stages in water bodies of the productive region and, therefore,water quality preservation is of great importance. An integrated pest management approach is currently being implemented to reduce the utilization of OP pesticides to meet the international requirements regarding the maximum residue levels of pesticides on fruit and to protect environmental health. Although polyamines (PA) are recognized as essential polycations for the normal progression of embryonic development and that their levels are consequently highly regulated, almost no studies have been conducted to analyze the influence of pesticides on PA metabolism. Considering the relevant role that amphibians play in the health of ecosystems, our objective is to analyze PA metabolism in R. arenarum embryos exposed to sublethal (0,5- and 2 mg/L) and lethal (9 mg/L) concentrations of AM. Control PA levels continuously increased along with embryonic development. AM exposure resulted in a significant increase in the number of malformed individuals, increased ornithine decarboxylase activity 18-fold and altered PA levels at the end of embryonic development: putrescine increased (60%) while spermidine and spermine decreased (56% and not detectable, respectively). Besides, our aim is to establish whether oxidative stress is related to PA metabolism, particularly, through their oxidative degradation. In this regard,we are currently investigating the effects of AM on the activity of N1-acetylpolyamineoxidase and diamine oxidase, according to Goodwin et al. (2011). Oxidative stress evidences were gradually observed during exposure to AM in the significant decrease of reduced glutathione and the inhibition of superoxide dismutase. Besides, a transcriptomic analysis showed that several genes encoding enzymes involved in PA metabolism modify their expression when R. arenarum larvae are exposed to sublethal concentrations of OP pesticides. In conclusion, exposure to AM alters PA metabolism in amphibian embryos, both at a transcriptional and a biochemical level, resulting in a shift from spermidine and spermine to putrescine at the end of embryonic development. It remains to be determined if PA oxidative degradation significantly contributes to the observed alteration of the antioxidant defense system. AM poses a threat for amphibian embryos in their natural habitats by impacting diverse cellular processes since biochemical and morphological alterations could impair their ability to deal with an environmental stress situation.