Effects of cadmium on glutathione synthesis in hepatopancreas of freshwater crab, Sinopotamon yangtsekiense

Cadmium (Cd) is one of the most deleterious heavy metals in aquatic systems that could promote oxidative damage. To explore the effects of Cd exposure of a freshwater crab (Sinopotamon yangtsekiense) on hepatopancreatic glutathione (GSH) synthesis, crabs were exposed to the reagent with a dose range of 7.25-116.00 mg L(-1) for 48 h. The concentrations of GSH, oxidized glutathione (GSSG), NADPH and NADP(+), as well as the activities of enzymes involved in GSH synthesis, i.e. glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD), gamma-glutamylcysteine synthetase (gamma-GCS) were determined. Progressive depletion of cellular GSH content was observed with the increasing of Cd concentrations, while the level of GSSG remained constant. In response to Cd exposure, crabs showed significant induction of G6PD and NADPH, however, only up to moderate exposures. GR activity remained at a steady level at all exposure concentrations. The activity of gamma-GCS was significantly positively correlated with the Cd concentration. These results suggested that GSH synthesis could be activated against reactive oxygen species induced by lower Cd exposure; under the higher Cd exposure conditions, an inhibition of NADPH-dependant redox cycling and de novo GSH synthesis led to significant decrease in GSH content.