RESUMO
Understanding the toxic mechanisms by which organisms cope to environmental stressful conditions is a fundamental question for ecotoxicology. In this study, we evaluated biochemical responses and hydrocarbons bioaccumulation of the mangrove oyster Crassostrea brasiliana exposed for 96 h to four sublethal concentrations of diesel fuel water-accommodated fraction (WAF). For that purpose, enzymatic activities (SOD, CAT, GPx, GR, G6PDH, GST and GGT), HSP60 and HSP90 immunocontent and lipid peroxidation (LPO) levels were determined in the gill and digestive gland of oysters and related to the hydrocarbons accumulated in the whole soft tissues. The results of this study revealed clear biochemical responses to diesel fuel WAF exposure in both tissues of the oyster. The capacity of C. brasiliana to bioaccumulate aliphatic and aromatic hydrocarbons in a dose-dependent manner is a strong indication of its suitability as a model in biomonitoring programs along the Brazilian coast, which was also validated by the response of the antioxidant defenses, phase II biotransformation and chaperones. HSP60 levels and GGT activity were the most promising biomarkers in the gill, while GST and GR activities stood out as suitable biomarkers for the detection of diesel toxicity in the digestive gland. The decrease of SOD activity and HSP90 levels may also reflect a negative effect of diesel exposure regardless the tissue. The present results provide a sound preliminary report on the biochemical responses of C. brasiliana challenged with a petroleum by-product and should be carefully considered for use in the monitoring of oil and gas activities in Brazil.
Assuntos
Crassostrea/metabolismo , Gasolina/toxicidade , Hidrocarbonetos Alicíclicos/toxicidade , Hidrocarbonetos Policíclicos Aromáticos/toxicidade , Poluentes Químicos da Água/toxicidade , Animais , Antioxidantes/metabolismo , Biomarcadores/metabolismo , Sistema Digestório/efeitos dos fármacos , Sistema Digestório/metabolismo , Relação Dose-Resposta a Droga , Brânquias/efeitos dos fármacos , Brânquias/metabolismo , Hidrocarbonetos Alicíclicos/farmacocinética , Peroxidação de Lipídeos/efeitos dos fármacos , Desintoxicação Metabólica Fase II , Estresse Oxidativo , Hidrocarbonetos Policíclicos Aromáticos/farmacocinética , Análise de Componente Principal , Poluentes Químicos da Água/farmacocinéticaRESUMO
The effect of the water-soluble fraction of crude oil (WSF) on lipid metabolism was studied at critical metabolic points, namely fatty acid activation, enzymes of triacylglycerol and phospholipid synthesis, and membrane (lipid packing) properties in the freshwater prawn Macrobrachium borellii. To determine the effect of the contaminant, adults and embryos at different stages of development were exposed to a sublethal concentration of WSF for 7 days. After exposure, microsomal palmitoyl-CoA synthetase (ACS) showed a two-fold increase in adult midgut gland. Embryo's ACS activity was also affected, the increment being correlated with the developing stage. Endoplasmic reticulum acylglycerol synthesis was also increased by WSF exposure in adults and stage 5 embryos, but not at earlier stages of development. Triacylglycerol synthesis was particularly increased (18.5%) in adult midgut gland. The microsomal membrane properties were studied by fluorescent steady-state anisotropy, using the rotational behavior of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Microsomes from midgut gland of WSF-exposed prawn showed no differences in fluidity. Nevertheless, microsomes incubated with WSF in vitro increased their fluidity in a temperature- and WSF concentration-dependent fashion. Both, aliphatic and aromatic hydrocarbons individually tested elicited an increase in membrane fluidity at 10 mg/l, but at 4 mg/l only nC10-C16 aliphatics did. In vivo results indicate that WSF increased the activity of microsomal enzymes that are critical in lipid metabolism, though this change was not due to direct alterations in membrane fluidity, suggesting a synthesis induction, or an enzyme-regulatory mechanism. Nevertheless, hydrocarbons elicited membrane fluidity alterations in in vitro experiments at concentrations that could be found in the environment after an oil spill.