The Role Of Glutathione-S-transferase In Resistance Mechanism Of Crassostrea Ariakensis To Diarrhetic Shellfish Poisoning Toxins

Glutathione-S-transferases(GST) are phase II enzymes that facilitate t he detoxification of xenobiotics, which catalytic reducing glutathione(GSH)-xenobiotics conjugate complex, again transported by ATP-bindingcassette transporter so as to achieve the aim of removing poison and exogenous subatances, at the same time GST play important roles in antioxidant defense.Here, to explore the roles of GST in resistant mechanism and detoxification of DSP toxins in shellfish, changes in eight GSTs m RNA level including GST-α, GST-ζ, GST-ω, GST-π, GST-μ, GST-ρ, GST-θ and microsomal GST(m GST) in the oyster Crassostrea ariakensis after exposure to P. lima were evaluated by quantitative real-time PCR(q PCR). Some GSTs isoforms contents and total GSTs enzyme activities were detected. Additionally, the accumulation of OA, P-gp and MRP activity and antioxidant system in gills of C. ariakensis were detected after exposure to P. lima in the presence or absence of GSTs inhibitors ethacrynic acid.After exposure to P. lima at density of 2×105 cells/L, GST-π, GST-μ, GST-θ, GST-ζ and m GST m RN A significantly increased in gill compared with control counterparts(p<0.05), while only GST-α and GST-ζ were induced in digestive gland(p<0.05). After exposure to P. lima at density of 2×106 cells/L, GST-θ and m GST expressions increased in gill(p<0.05), whereas GST-ω, GST-α, GST-π, GST-ζ and m GST were induced in digestive gland(p<0.05). The GST content and activity in oysters exposed to P. lima also showed a different pattern when the different isoforms and organs were compared. After exposure to P. lima(2×106 cell/L), GST-π increased in gill but decreased in digestive gland. The total GST enzyme activity increased in gill(p<0.05), while remained unchanged in digestive gland. These various regulation of GST gene expressions indicated that the GSTs isoenzymes might play divergent physiological roles during the detoxification of DSP toxins in C. ariakensis. Coupled with the oxidative stress in bivalves induced by P. lima and associated DSP toxins as reported by previous literatures, our results suggested that GST might play an important role in protecting cel s from oxidative stress induced by P. lima and associated DSP toxins..The addition of ethacrynic acid, GST activity and OA accumulation significantly decreased in gill and digestive gland of C. ariakensis. However the activity of P-gp and MRP significantly increased in gill. In conclusion, our results showed that P. lima exposure caused differential expressions and changes in content of GST isoforms. Coupled with the oxidative stress and peroxidation injury in bivalves induced by P. lima and associated DSP toxins as reported by previous literature, the changes in GST activity suggested that GST might play an important role in protecting cells from oxida tive stress induced by P. lima and associated DSP toxins.