Influence of a Toxic <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> Strain on Glutathione Synthesis and Glutathione-S-Transferase Activity in Common Carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis> (Teleostei: Cyprinidae) |
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Authors: | Lílian Lund Amado Márcia Longaray Garcia Patrícia Baptista Ramos João Sarkis Yunes José Maria Monserrat |
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Institution: | 1.Curso de Pós-Gradua??o em Ciências Fisiológicas-Fisiologia Animal Comparada,Universidade Federal do Rio Grande-FURG,Rio Grande,Brazil;2.Instituto de Ciências Biológicas (ICB),Universidade Federal do Rio Grande-FURG,Rio Grande,Brazil;3.Unidade de Pesquisa em Cianobactérias,FURG,Rio Grande,Brazil |
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Abstract: | We evaluated the effects of aqueous extracts of the cyanobacterium-producing microcystin (MC), Microcystis aeruginosa (strain RST9501), on detoxification capacity and glutathione (GSH) synthesis in liver, brain, gill, and muscle—as well as
apoptotic protease (calpain) activity in liver and brain—in the common carp Cyprinus carpio (Teleostei: Cyprinidae). Experimental groups were defined as follows: (1) control (CTR); (2) carp treated with an aqueous
extract from the toxic cyanobacteria M. aeruginosa in a final MC concentration of 25 μg/kg (MC 25); and (3) carp treated with an aqueous extract from the toxic cyanobacteria
M. aeruginosa in a final MC concentration of 50 μg/kg (MC 50). Carp were gavaged with a cyanobacterial aqueous solution or MilliQ water
(CTR group). The experiment was conducted for period of 48 h comprising two gavages with a 24-h interval between them. Some
of the parameters analyzed in liver, brain, gill, and muscle included activity of the enzymes glutathione-S-transferase (GST),
glutamate cysteine ligase (GCL), glutathione reductase (GR), and GSH concentration. We also evaluated GST pi concentration
by Western blot as well as calpain activity in liver and brain samples. In carp liver from the MC 50 group, we observed a
decrease in GST and GCL activity, which was accompanied by a decreased GSH concentration. In addition, liver calpain activity
was highly induced in carp at both MC doses. Thus, MC ingestion affected the liver antioxidant status through decreasing the
GSH concentration and the activity of the enzyme involved in its synthesis (GCL). It also decreased the MC detoxification
capacity of the liver because total GST activity decreased, a result that cannot be ascribed to GST pi levels. Because GSH
acts as an uncompetitive inhibitor of calpain, its decrease should explain the higher activity of this apoptotic enzyme. The
main goal of this study was to show that a decrease in GSH concentration is related to decreased activity of GCL, the limiting
enzyme involved in GSH synthesis. Because MCs are phosphatase inhibitors and GCL is allosterically inhibited by phosphorylation,
the cellular hyperphosphorylation state induced by MC exposure could act as a modulator factor for antioxidant defenses. |
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