Efeitos do metilfenidato sobre o sistema dopaminérgico, comportamento e estresse oxidativo em Oreochromis niloticus
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Data
2018-10-26
Autores
Batalhão, Isabela Gertrudes
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Universidade Estadual Paulista (Unesp)
Resumo
A ocorrência de fármacos no meio aquático tem aumentado consideravelmente nas últimas décadas, causando efeitos bioquímicos, fisiológicos e comportamentais em organismos aquáticos. Geralmente, a poluição aquática por fármacos ocorre como consequência das estações de tratamento de águas residuais (ETAR) não serem projetadas para remover completamente esses compostos dos efluentes, que por fim têm como destino as águas superficiais. O metilfenidato (MF, princípio ativo do medicamento ritalina®) é um estimulante do sistema nervoso central, recomendado para pessoas com transtorno do déficit de atenção e hiperatividade (TDAH), age inibindo os transportadores de recaptação da dopamina (3,4-dihidroxi-feniletanamina; DA), afim de aumentar os níveis desse neurotransmissor na fenda sináptica. Estudos já detectaram em efluentes a presença do MF e seu metabólito, o ácido ritalínico, em concentrações de ng.L-1. Com isso, o presente trabalho avaliou os efeitos bioquímicos, moleculares e comportamentais que o MF, em concentrações ambientalmente relevantes, pode causar em machos de tilápia do Nilo (Oreochromis niloticus). Peixes machos foram expostos a 0, 20,100 e 200 ng.L-1 de MF por 5 dias. Foram avaliados os efeitos do MF no comportamento agressivo, no sistema dopaminérgico e serotoninérgico, além nos níveis de transcritos de carboxilesterase e dos receptores de dopamina e na atividade da carboxilesterase (CbE) no encéfalo das tilápias expostas à concentração de 20 e 100 ng.L-1 de MF. Além disso, avaliamos enzimas do sistema de defesa antioxidante, enzimas de biotransformação, níveis de peroxidação lipídica e atividade das esterases no fígado e nas brânquias dos peixes expostos a 20, 100 e 200 ng.L-1 de MF. Os resultados mostraram que embora o MF aumente a agressividade dos animais, este efeito parece não estar diretamente relacionado ao sistema dopaminérgico dos animais, dada a diminuição das concentrações de DA e a ausência de alterações nos níveis de transcrição dos receptores de dopamina e tirosina hidroxilase. Também não foi relacionado a alterações nos níveis plasmáticos de testosterona. Sugerimos que o aumento da agressividade pode ser uma consequência de uma diminuição significativa nos níveis de 5-HT e DA no cérebro, diminuindo o medo e aumentando a ansiedade dos animais. Os resultados também mostraram que o efeito da exposição ao MF foi mais expressivo nas brânquias do que no fígado das tilápias. Foi observado uma diminuição concentração-dependente tanto na atividade das enzimas antioxidantes como na atividade das acetilcolinesterase nas brânquias dos animais, o que pode ter deixado os animais mais suscetíveis ao estresse oxidativo e a efeitos de hiperestimulação do SNC, respectivamente. Observarmos também, uma possível metabolização do fármaco devido ao aumento da CbE nas brânquias dos animais, porém, não houve alterações nas enzimas de biotransformação. A diminuição na peroxidação lipídica no fígado reforça a ausência de indução do sistema antioxidante mediante ao fármaco. Dessa forma, com o aumento do consumo global de diferentes classes de fármacos e a remoção incompleta desses compostos por ETAR, nossos resultados reforçam a importância de estudos que avaliem os riscos que os fármacos, em concentrações ambientalmente realísticas, podem causar em organismos não alvo, assim como, a importância de uma melhor eficiência na remoção dos fármacos pelos processos convencionais de tratamento dos efluentes.
The occurrence of pharmaceuticauls in the aquatic environment has increased in the last decades, causing biochemical, physiological and behavioral effects in aquatic organisms. In general, water pollution by pharmaceuticauls occurs because wastewater treatment plants (WWTPs) are not planned to completely remove these compounds from effluents, releasing these compounds to the surface water. Methylphenidate (MF, main ingredient of ritalin®,) is a central nervous system stimulant, recommended for people with attention deficit hyperactivity disorder (ADHD), which acts inhibiting dopamine recapitation transporters (3,4dihydroxyphenylethanamine; DA ), in order to increase the levels of this neurotransmitter in the synaptic cleft. Studies have already detected the presence of MF and its metabolite, ritalinic acid, in effluents in the concentrations of ng.L-1. Thus, the present study evaluated biochemical, molecular and behavioral effects that MF, in environmentally relevant concentrations, can cause in male Nile tilapia (Oreochromis niloticus). Male fish were exposed to 0, 20, 100 and 200 ng.L-1 of MF for 5 days. We evaluated the effects of MF on aggressive behavior, dopaminergic and serotoninergic system, in addition to the carboxylesterase and dopamine receptor transcript levels and carboxylesterase (CbE) activity in the brain of tilapias exposed to the concentration of 20 and 100 ng.L-1 of MF. Furthermore, we evaluated enzymes from the antioxidant defense system, biotransformation, lipid peroxidation levels and esterases activity in the liver and gills of fish exposed to 20, 100 and 200 ng.L-1 MF. The results showed that, although MF increases the aggressiveness of the animals, this effect does not appear to be directly related to the dopaminergic system of the animals, due to the decrease in DA levels and the absence of changes in the transcript levels of DA receptors and tyrosine hydroxylase. It was also not related to changes in plasma levels of testosterone. We suggest that increased aggressiveness may be a consequence of a significant decrease in serotonine (5-HT) and DA levels in the brain, decreasing fear and increasing anxiety in animals. The results also showed that effects of exposure to MF was more significant in the gills than in the liver of the Nile tilapia. A concentrationdependent decrease in both antioxidant enzyme activity and acetylcholinesterase activity in gills was observed, which may have made the animals more susceptible to oxidative stress and CNS hyperstimulation, respectively. We also observed a possible metabolism of the drug due to the increase of the CbE activity in the gills of the animals, but not changes was observed in the biotransformation enzymes. The decrease in lipid peroxidation in the liver reinforces the absence of induction of the antioxidant system by the drug. However, with increasing global consumption of different classes of drugs and incomplete removal of these compounds by WWTP, our results emphasize the importance of studies that assess the risks that drugs in environmentally realistic concentrations can cause in non-target organisms, as well as the importance of better efficiency in the removal of drugs by conventional effluent treatment processes.
The occurrence of pharmaceuticauls in the aquatic environment has increased in the last decades, causing biochemical, physiological and behavioral effects in aquatic organisms. In general, water pollution by pharmaceuticauls occurs because wastewater treatment plants (WWTPs) are not planned to completely remove these compounds from effluents, releasing these compounds to the surface water. Methylphenidate (MF, main ingredient of ritalin®,) is a central nervous system stimulant, recommended for people with attention deficit hyperactivity disorder (ADHD), which acts inhibiting dopamine recapitation transporters (3,4dihydroxyphenylethanamine; DA ), in order to increase the levels of this neurotransmitter in the synaptic cleft. Studies have already detected the presence of MF and its metabolite, ritalinic acid, in effluents in the concentrations of ng.L-1. Thus, the present study evaluated biochemical, molecular and behavioral effects that MF, in environmentally relevant concentrations, can cause in male Nile tilapia (Oreochromis niloticus). Male fish were exposed to 0, 20, 100 and 200 ng.L-1 of MF for 5 days. We evaluated the effects of MF on aggressive behavior, dopaminergic and serotoninergic system, in addition to the carboxylesterase and dopamine receptor transcript levels and carboxylesterase (CbE) activity in the brain of tilapias exposed to the concentration of 20 and 100 ng.L-1 of MF. Furthermore, we evaluated enzymes from the antioxidant defense system, biotransformation, lipid peroxidation levels and esterases activity in the liver and gills of fish exposed to 20, 100 and 200 ng.L-1 MF. The results showed that, although MF increases the aggressiveness of the animals, this effect does not appear to be directly related to the dopaminergic system of the animals, due to the decrease in DA levels and the absence of changes in the transcript levels of DA receptors and tyrosine hydroxylase. It was also not related to changes in plasma levels of testosterone. We suggest that increased aggressiveness may be a consequence of a significant decrease in serotonine (5-HT) and DA levels in the brain, decreasing fear and increasing anxiety in animals. The results also showed that effects of exposure to MF was more significant in the gills than in the liver of the Nile tilapia. A concentrationdependent decrease in both antioxidant enzyme activity and acetylcholinesterase activity in gills was observed, which may have made the animals more susceptible to oxidative stress and CNS hyperstimulation, respectively. We also observed a possible metabolism of the drug due to the increase of the CbE activity in the gills of the animals, but not changes was observed in the biotransformation enzymes. The decrease in lipid peroxidation in the liver reinforces the absence of induction of the antioxidant system by the drug. However, with increasing global consumption of different classes of drugs and incomplete removal of these compounds by WWTP, our results emphasize the importance of studies that assess the risks that drugs in environmentally realistic concentrations can cause in non-target organisms, as well as the importance of better efficiency in the removal of drugs by conventional effluent treatment processes.
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Palavras-chave
Fármaco, Biomarcadores, Neurotransmissores, Agressividade, Tilápias do Nilo, Pharmaceuticauls, Biomarkers, Neurotransmitters, Aggressiveness, Nile tilapia