Interference the fipronil insecticide on responses on oxidative stress of Tilapia Nile mediated by gamma-aminobutyric acid (GABA) during periods of hypoxia.

Author(s)

Priscila Leocadia Rosa Dourado

• Document type: Doctoral Thesis
• Press: São José do Rio Preto. 2019-05-09.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências Letras e Ciências Exatas. São José do Rio Preto
• Defense date: 2019-04-08
• Advisor: Claudia Regina Bonini Domingos; Danilo Grünig Humberto da Silva

Abstract

Regent®800WG is one of the most used insecticides in the cultivation of sugarcane in Brazil and has as active principle fipronil. Fipronil exerts its insecticidal activity by competing with GABA for GABA-a receptor binding sites, blocking chloride channels and preventing the transmission of normal nervous impulse, which leads to inhibition of neuronal transmission and induces neuronal hyperexcitation. Fipronil is a persistent soil compound and has been widely detected in aquatic environments. In natural environments the action and effects of this type of compound can be influenced by different environmental aspects, such as variations in water temperature, pH, salinity and dissolved oxygen. Similar, the effects of environmental pollutants can modify the adaptations of the animals to these environmental variables, raising the mortality risks face to adversity in the ecosystem. Thus, this study aimed to investigate the influence of fipronil (Regent®800WG) in fish exposed to hypoxia and different temperatures, on the oxidative stress parameters, DNA damage, gene transcription levels, as well sex hormones levels. Our first study investigated the influence of fipronil (0.1 µg.L-1 and 0.5 µg.L-1) in the brain, in oxidative stress markers of gills and liver, and genotoxic effects on erythrocytes of Oreochromis niloticus submitted to hypoxia for 3 and 8 hours. In our second study, we aimed to evaluate on the effects of food administration of Fipronil (Regent®800WG) under two temperatures was carried out in the sea bass (Dicentrarchus labrax) for 21 days. Our results showed that the antioxidant defense systems in gills and liver of the fish remained elevated during the first 3 hours of exposure, probably to adapt to hypoxic stress conditions. In the groups exposed to fipronil, the concentrations and times influenced the antioxidant defense system, altering the antioxidant enzymes activity (CAT and GR), and the GST biotransformation enzyme. The results also allowing us to observe that the mechanisms of detoxification were specific for each tissue, and the most representative alterations were found in the gills. In the brain, the levels of GABA, HIF-1A, and antioxidant enzyme CAT transcript levels showed negative regulation for all groups after 3 h of exposure, however, after 8 h the transcript levels showed a return to control levels except for GABA-b1 receptor in the group exposed to fipronil (0.5 μg.L-1) in the presence of hypoxia. The results of the study with sea bass (D. labrax) revealed that fipronil administered in food under influence of different temperatures, impaired the metabolic and antioxidant responses of exposed animals, as well influenced the regulation of sex hormones (E2, T, 11-KT). These results suggest a response by the animal body to balance the initial negative effects of treatments, which could be affected by the presence of contaminants or environmental variables (hypoxia, temperature). Our results showed that the exposure to environmental stressors combined caused greater disturbances in the biochemical, physiology and neuronal responses of the fish when compared to the individual factors, as well to induce genotoxic damage and lipid peroxidation in fish tissues, reinforcing the importance of evaluating the damage which chemical contaminants can cause to non-target species such as fish, and better understand how these contaminants interfere with the adaptive mechanisms of fish to stressful situations such as hypoxia. (AU)

• FAPESP's process: 15/15191-1 - Interference the fipronil insecticide on responses on oxidative stress of Tilapia Nile mediated by gamma-aminobutyric acid (GABA) during periods of hypoxia.
• Grantee: Priscila Leocadia Rosa Dourado
• Support Opportunities: Scholarships in Brazil - Doctorate