Sistema de defesa antioxidante na larva do quironomídeo Tanytarsus minutipalpus: Adaptação às condições ambientais extremas do Lago Magadi (Quênia, África)

Abstract

Foram avaliadas alterações no metabolismo e no sistema de defesa antioxidante na larva do quironomídeo Tanytarsus minutipalpus frente a variações diárias e extremas nas condições físico-químicas no "Flamingo Pool" no Lago Magadi (Quênia). Em diferentes horas do dia (7:00 h, 13:00 h e 19:00 h do mesmo dia e 1:00 h e 7:00 h do dia seguinte), em diferentes dias de Julho/Agosto de 2010 e Julho de 2013, foram medidos a temperatura, teor de oxigênio dissolvido e pH da água. As larvas de T. minutipalpus foram coletadas com rede de zooplâncton, separadas manualmente e utilizadas para análise de parâmetros metabólicos (atividade da colinesterase e concentrações de glicose, triglicerídeos, colesterol, proteínas, uréia, hemoglobina e bilirrubina) e do estado oxidativo [espécies reativas de oxigênio (ROS), óxido nítrico (NO), glutationa reduzida (GSH), glutationa oxidada (GSSG), mucoproteínas, superóxido dismutase (SOD), catalase (CAT), glutationa peroxidase (GPx), glutationa redutase (GR), glutamato-cisteína ligase (GCL), capacidade antioxidante total (TOSC), lipoperoxidação (LPO) e dano no DNA]. Não houve variação no pH (10.0 ± 0.03) da água, porém foram observadas amplas variações diárias de temperatura (20.2-29.3oC) e oxigênio dissolvido (3.2-18.6 mg O2/L), com os valores médios mais altos sendo observados às 13:00 h. Foram observados aumentos temporários na colinesterase, glicose, colesterol, ureia, creatinina, hemoglobina SOD, GPx, GR, GSH e GSSG nas larvas coletadas às 13:00 h. Estes resultados indicam que a larva de T. minutipalpus apresenta ajustes metabólicos e no sistema de defesa antioxidante que respondem positivamente e de forma cooperativa frente às variações diárias e extremas na temperatura e oxigênio dissolvido nas águas do Lago Magadi.

In the present study, we report for the first time the occurrence of the immature chironomid Tanytarsus minutipalpus in the Lake Magadi (Kenya, Africa). Adaptive responses in metabolism and antioxidant defense system to the diel variations in the extreme environmental conditions of the Lake Magadi were evaluated in chironomid larvae. In July-August 2010 and 2013, we performed measurements of water physicochemical parameters (temperature, dissolved oxygen and pH) and chironomid sampling at different times of day (7:00 am, 1:00 pm and 7:00 pm of the first day; and 1:00 am and 7:00 am of the following day). Larvae were collected using a bean trawl net (90-µm mesh), manually separated and immediately placed in liquid nitrogen or quickly transferred to laboratory for analyses of parameters indicative of metabolism (cholinesterase activity and glucose, triglycerides, cholesterol, proteins, urea, creatinine, hemoglobin and bilirubin concentration), pro-oxidant status [reactive oxygen species (ROS) and nitric oxide (NO) concentration], antioxidant status [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutamate-cysteine ligase (GCL) activity, as well as total glutathione (GSH), oxidized glutathione (GSSG) and mucoproteins concentration], and oxidative status [total antioxidant capacity (TOSC), lipid peroxidation (LPO) and DNA damage]. Wide variations in water temperature (20.2-29.3oC) and dissolved oxygen (3.2-18.6 mg O2/L) were observed at different times of day, without any significant change in water pH (10.0 ± 0.03). Higher mean values of water temperature and dissolved oxygen were observed at 1:00 pm (29.3 ± 0.8oC and 18.6 ± 1.0 mg O2/L, respectively) and 7:00 pm (29.3 ± 1.4oC and 16.2 ± 1.6 mg O2/L, respectively). Significant increases in parameters related to metabolism (cholinesterase, glucose, cholesterol, urea, creatinine and hemoglobin) paralleled by significant increases in the major components of the 19 antioxidant system (SOD, GPx, GR, GSH and GSSG) were observed in chironomid larvae collected at 1:00 pm. On the other hand, no significant changes were observed in pro-oxidants (ROS and NO), TOSC and oxidative damage parameters (LPO and DNA damage). These findings clearly show that the antioxidant system of T. minutipalpus larvae acts positively and cooperatively to face an increased metabolism in response to increasing temperature and O2 content in Lake Magadi waters. They also indicate that biochemical and physiological adjustments performed by the chironomid larvae were efficient in keeping body homeostasis, as well as protecting biomolecules against oxidative damage. GSH-GSSG and GPx-GR systems were shown to play an essential role in the adaptive response displayed by the chironomid larvae when facing the diel changes in the extreme conditions of the Lake Magadi.