Interferência do inseticida fipronil nas respostas ao estresse oxidativo de Tilápias do Nilo mediadas pelo ácido gama aminobutírico (GABA), durante períodos de hipóxia.
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Data
2019-04-08
Autores
Dourado, Priscila Leocadia Rosa
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Universidade Estadual Paulista (Unesp)
Resumo
O Regent®800WG é um dos inseticidas mais utilizados no cultivo de cana-de-açúcar no Brasil e apresenta como princípio ativo o fipronil. O fipronil apresenta alta capacidade de interação com os receptores do ácido gama-aminobutírico (GABA), sendo que seu principal mecanismo de ação é competir com o GABA pelos canais de cloro, resultando em excitabilidade. O fipronil é um composto persistente no solo e tem sido amplamente detectado em ambientes aquáticos. Em ambientes naturais a ação e efeitos desse tipo de composto podem ser influenciados por diferentes aspectos ambientais, como variações na temperatura da água, pH, salinidade e oxigênio dissolvido. Da mesma forma, os efeitos de poluentes ambientais podem alterar as adaptações dos animais frente a essas variações ambientais, elevando os riscos de mortalidade frente adversidades do ecossistema. Assim, o presente trabalho objetivou avaliar a influência da exposição a uma formulação comercial do fipronil (Regent®800WG) em peixes expostos à hipóxia e à diferentes temperaturas, utilizando parâmetros de estresse oxidativo, danos ao DNA, níveis de transcrição gênica, bem como concentração de hormônios sexuais. No primeiro estudo objetivou avaliar a influência da exposição ao fipronil (Regent®800WG) nas concentrações 0,1 e 0,5 µg.L-1, no encéfalo, em parâmetros de estresse oxidativo nas brânquia e fígado e os efeitos genotóxicos em eritrócitos de Oreochromis niloticus submetidos à hipóxia for 3 e 8 horas. Em um segundo trabalho, objetivamos avaliar a influência do fipronil administrado na comida em respostas bioquímicas de robalos (Dicentrarchus labrax) sob diferentes temperaturas. Os resultados mostraram que os sistemas de defesa antioxidantes dos peixes permaneceram elevados durante as primeiras 3 horas de exposição, possivelmente para se adaptar às condições de estresse hipóxico. Nos grupos expostos ao fipronil, as concentrações e os tempos de exposição influenciaram o sistema de defesa antioxidante, alterando a atividade das enzimas antioxidantes CAT, GR e da enzima de biotransformação GST. Os resultados também nos permitiram observar que os mecanismos de desintoxicação foram específicos para cada tecido, sendo as alterações mais representativas encontradas nas brânquias. No cérebro, observamos que os níveis de transcritos dos receptores GABA, do HIF-1A e da enzima antioxidante CAT, mostraram um regulação negativa para todos os grupos após 3 h de exposição, porém, no decorrer do tempo de exposição os níveis de transcrição mostraram voltar aos níveis basais, exceto no receptor GABAb1 no grupo exposto ao fipronil (0,5 µg.L-1) na presença de hipoxia. Os resultados do estudo feito com robalos (D. labrax) reveleram que o fipronil administrado na comida, sob a influência de diferentes temperaturas, prejudicou as respostas metabólicas e antioxidantes dos animais expostos, bem como influenciou na regulação dos hormônios sexuais (E2, T, 11-KT). Esses resultados sugerem uma resposta do corpo do animal para balancear os efeitos negativos iniciais dos tratamentos, que possivelmente foram afetados pela presença de contaminantes ou das variáveis ambientais (hipóxia, temperatura). A exposição aos estressores ambientais combinados, causou maior distúrbio nas respostas bioquímicas, fisiológicas e neuronais dos peixes quando comparados aos fatores individuais, bem como foram capazes de induzir dano genotóxico e peroxidação lipídica nos tecidos dos peixes, reforçando a importância de avaliar os prejuízos que contaminantes químicos podem causar à espécies não-alvo, como peixes, e melhor compreender como esses contaminantes interferem nos mecanismos adaptativos dos peixes à variações nas condições ambientais.
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.
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.
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Palavras-chave
Pesticidas, Efeitos ambientais, Neurotoxicidade, Biomarcadores, Peixes, Pesticides, Environmental effects, Neurotoxicity, Biomarkers, Fish